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| author | Elizabeth Alexander Hunt <me@liz.coffee> | 2026-07-02 11:55:17 -0700 |
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| committer | Elizabeth Alexander Hunt <me@liz.coffee> | 2026-07-02 11:55:17 -0700 |
| commit | 6bf4b90c90f15f4ab60833bddf5b5756d1a6b1f6 (patch) | |
| tree | ed97e39ec77c5231ffd2c394493e68d00ddac5a4 /Homework/math4310 | |
| download | misc-undergrad-main.tar.gz misc-undergrad-main.zip | |
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diff --git a/Homework/math4310/1.pdf b/Homework/math4310/1.pdf Binary files differnew file mode 100644 index 0000000..c0dd6fb --- /dev/null +++ b/Homework/math4310/1.pdf diff --git a/Homework/math4310/1.tex b/Homework/math4310/1.tex new file mode 100644 index 0000000..f66b8a5 --- /dev/null +++ b/Homework/math4310/1.tex @@ -0,0 +1,240 @@ +% Created 2023-01-18 Wed 12:13 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\noindent \notag \usepackage{ dsfont } +\author{Logan Hunt} +\date{\today} +\title{Assignment One} +\hypersetup{ + pdfauthor={Logan Hunt}, + pdftitle={Assignment One}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.5.5)}, + pdflang={English}} +\begin{document} + +\maketitle +\tableofcontents + + +\section{Section 1.1} +\label{sec:org35f7eb6} +\subsection{Question 5} +\label{sec:orge503259} +By reforming the given expression to show \(ca\) as a multiple of \(q\) and some remainder: + +\begin{align} +a = bq + r \\ +ca = (cb)q + (c)r +\end{align} + +and that \(0 \leq r < b \Rightarrow 0 \leq cr < cb\), Theorem 1.1 tells us that there is only one unique quotient: +which is \(q\), and the remainder is \((c)r\). + +\subsection{Question 7} +\label{sec:org6afde38} +By Theorem 1.1, \(a = bq + r, 0 \leq r \lt b\) implies that when b = 3, \(a = 3q + r\) where \(0 \leq r \lt b\), +thus \(a \in \mathds{Z} \Rightarrow a = 3q + r\) where \(r \in {0,1,2}\). + +By squaring \(a\), we have three options which simplify to the form \(3k\) or \(3k + 1\): +\begin{enumerate} +\item \(a^2 = (3q)^2 = 9q^2\) which is \(3k \ni k = 3q^2\) +\item \(a^2 = (3q + 1)^2 = 9q^2 + 3q + 1 = 3(3q^2 + q) + 1\) which is \(3k + 1 \ni k = (3q^2 + q)\) +\item \(a^2 = (3q + 2)^2 = 9q^2 + 6q + 4 = 3(3q^2 + 2q) + 4\) which is +\(3l + 4 \ni l = (3q^2 + 2q)\) which is also \(3l + 1 + 3 = 3(l+1) + 1\), +which again is \(3k + 1 \ni k = l+1\) +\end{enumerate} + +\subsection{Question 8} +\label{sec:orgfe8a512} +By Theorem 1.1, \(a = bq + r, 0 \leq r \lt b\) implies that when b = 4, \(a = 4q + r\) where \(0 \leq r \lt b\), +and thus \(a = 4q + r\) and \(r \in {0,1,2,3}\). + +Therefore we have four cases: + +\begin{enumerate} +\item \(a = 4q\), and \(a\) must be even which is invalid +\item \(a = 4q + 1\), and \(4q + 1 = 2k + 1 \ni k = 2q\) which fits the definition of an odd number +\item \(a = 4q + 2\), thus \(a\) must be even as \(a = 2k \ni k = 2q + 1\) +\item \(a = 4q + 3\), can be rewritten to \(4q + 1 + 2\), which is odd: \(2k + 1 \ni k = 2q + 1\) +\end{enumerate} + +And thus any odd number can be rewritten as \(4q + 1\) or \(4q + 3\). + +\subsection{Question 10} +\label{sec:org3c66372} +The division of \(a\) and \(c\) by \(n\) can each be represented by + +\begin{align} +a = q_{a}n + r_a \\ +c = q_c_{}n + r_c +\end{align} + +where \(0 \le r_a < n\) and \(0 \le r_c < n\) by Theorem 1.1, and we can subtract each side of the +second equation from the first: + +\begin{align} +a - c = (q_{a}n + r_a) - (q_c_{}n + r_c) +\end{align} + +With this work now in hand, we will prove by showing that the conjecture is true both ways: + +For the first, we will suppose that \(r_a = r_c\). Then, we find that +\begin{align} +a - c = n(q_a - q_c) \\ +a - c = nk +\end{align} +for some integer \(k\). + +For the second, we will prove that if \(a - c = nk\), when \(a\) and \(c\) are divided by \(n\), +they leave the same remainder \(r\). + +From the work we did previously, and by substituting \(a-c = nk\), we find that +\begin{align} +a - c = (q_{a}n + r_a) - (q_c_{}n + r_c) \\ +nk = (q_{a}n + r_a) - (q_{c}n + r_c) \\ +nk = n(q_a - q_c) + (r_a - r_c) \\ +n(k - q_a + q_c) = r_a - r_c +\end{align} +and thus \(r_a - r_c\) is a multiple of \(n\). + +From the inequalities produced previously by Theorem 1.1, if \(r_a \geq r_c\) then \(0 \le r_a - r_c < n\) +and \(-n < r_c - r_a \leq 0\). Else if \(r_c \geq r_a\) then \(0 \leq r_c - r_a < n\) and \(-n < r_a - r_c \leq 0\). + +By combining the two cases, it must be that \$ -n < r\textsubscript{a} - r\textsubscript{c} < n \$, and from the above fact that +\(r_a - r_c\) is a multiple of n, the only multiple of n in \((-n, n)\) is 0. Thus \(r_a = r_c\). + +\section{Section 1.2} +\label{sec:org4226083} +\subsection{Question 1} +\label{sec:org4ccc206} +\subsubsection{c} +\label{sec:org802af33} +1, 57 and 112 are co-prime +\subsection{Question 3} +\label{sec:orgb341781} +\begin{align} +a | b \Rightarrow \exists n \in \mathds{Z} \ni an = b \\ +b | c \Rightarrow \exists m \in \mathds{Z} \ni bm = c \\ +(an)m = c \Rightarrow a | c +\end{align} +\subsection{Question 4} +\label{sec:orge55e932} +\subsubsection{a} +\label{sec:org7540edc} +\begin{align} +a | b \Rightarrow \exists n \in \mathds{Z} \ni an = b \\ +a | c \Rightarrow \exists m \in \mathds{Z} \ni am = c \\ +a | (b + c) \Rightarrow \exists l \in \mathds{Z} \ni al = b + c \\ +al = an + am \\ +b + c = a(n + m) +\Rightarrow a | b+c +\end{align} +\subsubsection{b} +\label{sec:orge72f7c4} +By continuing from "a": + +\begin{align} +br + ct = (an)r + (am)t \\ +\Rightarrow br + ct = a(nr + mt) \\ +\Rightarrow a | (br + ct) +\end{align} + + +\subsection{Question 7} +\label{sec:org7273a90} +\(|a|\) since \(|a| \textbar a\) and \(|a| \textbar 0\), and there cannot be an integer larger than +\(|a|\) that divides \(a\). + +\subsection{Question 9} +\label{sec:org6b4815b} +No, not every multiple of two factors of an integer divides that integer. + +For example, \(3 | 9\) and \(9 | 9\) but \(27 \nmid 9\). + +\subsection{Question 15} +\label{sec:orgf96c6cd} +\subsubsection{c} +\label{sec:orgad14e2b} +\begin{align} +1003 = (2)(456) + 91 \\ +456 = (5)(91) + 1 \\ +91 = (91)(1) + 0 \\ +\Rightarrow (1003, 456) = 1 +\end{align} +\subsubsection{d} +\label{sec:orgf89fea4} +\begin{align} +322 = (2)(148) + 26 \\ +148 = (5)(26) + 18 \\ +26 = (1)(18) + 8 \\ +18 = (2)(8) + 2 \\ +8 = (4)(2) + 0 \\ +\Rightarrow (322, 148) = 2 +\end{align} + +\subsection{Question 17} +\label{sec:org66d011a} + +\begin{align} +a | c \Rightarrow \exists n \in \mathds{Z} \ni an = c \\ +b | c \Rightarrow b | an +\end{align} + +And by Theorem 1.4, \((a, b) = 1 \Rightarrow b | n \Rightarrow ab | an \Rightarrow ab | c\): + +\subsection{Question 19} +\label{sec:org905b244} +Given some \(d\) such that \(d | a\) and \(d | b\), then \(a = nd\) and \(b = md\). +\begin{align} +a | (b + c) \Rightarrow \exists p \in \mathds{Z} \ni ap = b + c \\ +c = ap - md \Rightarrow c = (nd)p - md \Rightarrow c = d(np - md) \Rightarrow d | c +\end{align} + +Since we're given that \((b, c) = 1 \Rightarrow (md, c) = 1\) and from the above fact that \(d | c\), we can conclude +that \(md = 1\). Therefore \((a, b) = (a, md) = (a, 1) = 1\). + +Given some \(e\) such that \(e | a\) and \(e | c\), then \(a = ue\) and \(c = we\). +\begin{align} +a | (b + c) \Rightarrow \exists o \in \mathds{Z} \ni ao = b + c \\ +b = ao - we \Rightarrow b = (ue)o - we \Rightarrow b = e(uo - w) \Rightarrow e | b +\end{align} + +And from similar reasoning we can conclude that \((a, c) = (a, we) = (a, 1) = 1\). + +\subsection{Question 31} +\label{sec:orgc12b666} +\subsubsection{a} +\label{sec:org4312735} +\([6, 10] = 60\) + +\([4, 5, 6, 10] = 60\) + +\([20, 42] = 840\) + +\([2, 3, 14, 36, 42] = 252\) + +\subsubsection{b} +\label{sec:orgb964c2c} +Let \(m = [a_1, a_2, \ldots, a_k]\), then by the Division Algorithm, \(t = mq + r\) for integers \(q\) and \(r\), +with \(0 \leq r < m\). + +As given that all \(a_i | t\) \(\Rightarrow\) \(a_i | mq + r\), and as \(mq\) is a multiple of the LCM including +a\textsubscript{i}, \(a_i\) must divide \(mq\), and thus \(a_i | r\). + +Because \(a_i | r\), \(r = na_i\) and is thus a multiple of all \(a_i\), but the above statement that +\(0 \leq r < m\) shows that \(m\) - the LCM by definition - is greater than \(r\). Therefore, \(r = 0\) and +\(t = mq \Rightarrow m | t\). +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/328e45ffe10876ae6e22f4d5a990f625-emacs-elixir-format.ex b/Homework/math4310/328e45ffe10876ae6e22f4d5a990f625-emacs-elixir-format.ex new file mode 100644 index 0000000..00d0d55 --- /dev/null +++ b/Homework/math4310/328e45ffe10876ae6e22f4d5a990f625-emacs-elixir-format.ex @@ -0,0 +1 @@ +File alg_structures_assn_4.pdf changed on disk. Reread from disk? (yes or no)
\ No newline at end of file diff --git a/Homework/math4310/abstract_algebra_assn_10.org b/Homework/math4310/abstract_algebra_assn_10.org new file mode 100644 index 0000000..99b288a --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_10.org @@ -0,0 +1,104 @@ +#+TITLE: Assignment Ten +#+AUTHOR: Lizzy Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} \usepackage{polynom} \usepackage{wasysym} +#+LATEX: \setlength\parindent{0pt} +#+OPTIONS: toc:nil + +* Section 6.1 +** Question Four +No. As a counterexample, suppose $n = \big(\begin{smallmatrix} + 0 & 0\\ + 0 & 1 +\end{smallmatrix}\big) \in J$, and $m = \big(\begin{smallmatrix} + 1 & 1 \\ + 1 & 1 +\end{smallmatrix}\big) \in M(\mathds{R})$, $mn = \big(\begin{smallmatrix} + 0 & 1 \\ + 0 & 1 +\end{smallmatrix}\big) \notin J$ + +** Question Five +By Theorem 3.6, $K$ is a subring since it is closed under subtraction: $\big(\begin{smallmatrix} + a & b \\ + 0 & 0 +\end{smallmatrix}\big) - +(\begin{smallmatrix} + c & d \\ + 0 & 0 +\end{smallmatrix}\big) = +(\begin{smallmatrix} + a - c & b - d \\ + 0 & 0 +\end{smallmatrix}\big)$, and absorbs products of $M(\mathds{R})$ on the right (which is a superset of $K$, so $K$ is closed under this multiplication): +$(\begin{smallmatrix} + a & b \\ + 0 & 0 +\end{smallmatrix}\big) \cdot +(\begin{smallmatrix} + c & d \\ + e & f +\end{smallmatrix}\big) += +(\begin{smallmatrix} + ac + be & ad + bf \\ + 0 & 0 +\end{smallmatrix}\big)$ + +But from the left, as a counterexample $n = (\begin{smallmatrix} +1 & 1 \\ +0 & 0 +\end{smallmatrix}\big) \in K, m =(\begin{smallmatrix} + 2 & 1 \\ + 3 & 0 +\end{smallmatrix}\big) \in M(\mathds{R})$, then $mn = (\begin{smallmatrix} + 2 & 2 \\ + 3 & 3 +\end{smallmatrix}\big) \notin K$ + +** Question Eleven +*** a +$(1) = (2) = (3) = (4) = \mathds{Z}_5$ and $(0) =$ { 0 } + +*** b +$(1) = (2) = (4) = (5) = (7) = (8) = \mathds{Z}_9$, $(0) =$ { 0 }, and $(3) = (6) =$ { 0, 3, 6 } + +*** c +$(1) = (5) = (7) = (11) = \mathds{Z}_{12}$, $(2) = (6) = (10) =$ { 0, 2, 4, 6, 8, 10 }, $(4) = (8) =$ { 0, 4, 8 }, +$(3) = (9) =$ { 0, 3, 6, 9 }, and $(6) =$ { 0, 6 } + +** Question Thirteen +No, $\mathds{Z}_5$ is a commutative ring, but in question above, $(1) = (2)$ but $1 \neq 2$. + +** Question Sixteen +*** a +If we can show that $(4, 6) \sube (2)$ and $(2) \sube (4, 6)$, then we can conclude that $(4, 6) = (2)$ + +Each element $x \in (4, 6) \Rightarrow x = 4m + 6n$ for $m,n \in \mathds{Z}$. + +Thus $x = 2(2m + 3n)$ which shows that $x$ is a multiple of two, and thus, $(4, 6) \sube (2)$. + +Each element $y \in (2) \Rightarrow y = 2p$ for $p \in \mathds{Z}$. When $p$ is itself a multiple of two, this can be rewritten as $y = 2(2o) = 4o$ and thus $y \in (4, 6)$. + +When $y$ is odd, $y = 2(2(q - 1) + 3) = 4q + 6$ for some $q \in \mathds{Z}$. Therefore, $y$ is in $(4, 6)$. + +*** b +We'll take the same approach as a: + +Each element $x \in (6, 9, 15) = 6m + 9n + 15o$ with $m, n, o \in \mathds{Z}$. + +Thus $x = 3(2m + 3n + 5o)$ is a multiple of three, so $x \in (3)$. + +Each element $y \in (3) \Rightarrow y = 3p$ for $p \in \mathds{Z}$. When $p$ is a multiple of two, then $y = 3(2q) = 6q \in (6, 9, 15)$. + +When $p$ is odd, $y = 3(2(u - 1) + 7)$ for some $u \in \mathds{Z}$, $y = 6u + 15 \in (6, 9, 15)$. + +** Question Seventeen +*** a +If $a \in I \cap J$, and $b \in I \cap J$, then $a \in I$, $b \in I$, $a \in J$, and $b \in J$. Then, $a - b \in I$ and $a - b \in J$, so +$a - b \in I \cap J$. + +If $a \in I \cap J$ and $r \in R$, then $ra \in I$, $ra \in J$, $ar \in J$, and $ar \in I$ by definition of I and J. + +Therefore, $I \cap J$ is an ideal in $R$. + diff --git a/Homework/math4310/abstract_algebra_assn_10.pdf b/Homework/math4310/abstract_algebra_assn_10.pdf Binary files differnew file mode 100644 index 0000000..aff4a61 --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_10.pdf diff --git a/Homework/math4310/abstract_algebra_assn_10.tex b/Homework/math4310/abstract_algebra_assn_10.tex new file mode 100644 index 0000000..83a3062 --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_10.tex @@ -0,0 +1,140 @@ +% Created 2023-04-16 Sun 21:55 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} \usepackage{polynom} \usepackage{wasysym} +\author{Lizzy Hunt} +\date{\today} +\title{Assignment Ten} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Assignment Ten}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Section 6.1} +\label{sec:org1d97e2b} +\subsection{Question Four} +\label{sec:orgd166f06} +No. As a counterexample, suppose \(n = \big(\begin{smallmatrix} + 0 & 0\\ + 0 & 1 +\end{smallmatrix}\big) \in J\), and \(m = \big(\begin{smallmatrix} + 1 & 1 \\ + 1 & 1 +\end{smallmatrix}\big) \in M(\mathds{R})\), \(mn = \big(\begin{smallmatrix} + 0 & 1 \\ + 0 & 1 +\end{smallmatrix}\big) \notin J\) + +\subsection{Question Five} +\label{sec:orgd391af3} +By Theorem 3.6, \(K\) is a subring since it is closed under subtraction: \(\big(\begin{smallmatrix} + a & b \\ + 0 & 0 +\end{smallmatrix}\big) - +(\begin{smallmatrix} + c & d \\ + 0 & 0 +\end{smallmatrix}\big) = +(\begin{smallmatrix} + a - c & b - d \\ + 0 & 0 +\end{smallmatrix}\big)\), and absorbs products of \(M(\mathds{R})\) on the right (which is a superset of \(K\), so \(K\) is closed under this multiplication): +\((\begin{smallmatrix} + a & b \\ + 0 & 0 +\end{smallmatrix}\big) \cdot +(\begin{smallmatrix} + c & d \\ + e & f +\end{smallmatrix}\big) += +(\begin{smallmatrix} + ac + be & ad + bf \\ + 0 & 0 +\end{smallmatrix}\big)\) + +But from the left, as a counterexample \(n = (\begin{smallmatrix} +1 & 1 \\ +0 & 0 +\end{smallmatrix}\big) \in K, m =(\begin{smallmatrix} + 2 & 1 \\ + 3 & 0 +\end{smallmatrix}\big) \in M(\mathds{R})\), then \(mn = (\begin{smallmatrix} + 2 & 2 \\ + 3 & 3 +\end{smallmatrix}\big) \notin K\) + +\subsection{Question Eleven} +\label{sec:orgd8049eb} +\subsubsection{a} +\label{sec:org51730ce} +\((1) = (2) = (3) = (4) = \mathds{Z}_5\) and \((0) =\) \{ 0 \} + +\subsubsection{b} +\label{sec:org3030fdd} +\((1) = (2) = (4) = (5) = (7) = (8) = \mathds{Z}_9\), \((0) =\) \{ 0 \}, and \((3) = (6) =\) \{ 0, 3, 6 \} + +\subsubsection{c} +\label{sec:orgac8d99a} +\((1) = (5) = (7) = (11) = \mathds{Z}_{12}\), \((2) = (6) = (10) =\) \{ 0, 2, 4, 6, 8, 10 \}, \((4) = (8) =\) \{ 0, 4, 8 \}, +\((3) = (9) =\) \{ 0, 3, 6, 9 \}, and \((6) =\) \{ 0, 6 \} + +\subsection{Question Thirteen} +\label{sec:org8889fae} +No, \(\mathds{Z}_5\) is a commutative ring, but in question above, \((1) = (2)\) but \(1 \neq 2\). + +\subsection{Question Sixteen} +\label{sec:org132058d} +\subsubsection{a} +\label{sec:org121e6c5} +If we can show that \((4, 6) \sube (2)\) and \((2) \sube (4, 6)\), then we can conclude that \((4, 6) = (2)\) + +Each element \(x \in (4, 6) \Rightarrow x = 4m + 6n\) for \(m,n \in \mathds{Z}\). + +Thus \(x = 2(2m + 3n)\) which shows that \(x\) is a multiple of two, and thus, \((4, 6) \sube (2)\). + +Each element \(y \in (2) \Rightarrow y = 2p\) for \(p \in \mathds{Z}\). When \(p\) is itself a multiple of two, this can be rewritten as \(y = 2(2o) = 4o\) and thus \(y \in (4, 6)\). + +When \(y\) is odd, \(y = 2(2(q - 1) + 3) = 4q + 6\) for some \(q \in \mathds{Z}\). Therefore, \(y\) is in \((4, 6)\). + +\subsubsection{b} +\label{sec:orgc2b77e9} +We'll take the same approach as a: + +Each element \(x \in (6, 9, 15) = 6m + 9n + 15o\) with \(m, n, o \in \mathds{Z}\). + +Thus \(x = 3(2m + 3n + 5o)\) is a multiple of three, so \(x \in (3)\). + +Each element \(y \in (3) \Rightarrow y = 3p\) for \(p \in \mathds{Z}\). When \(p\) is a multiple of two, then \(y = 3(2q) = 6q \in (6, 9, 15)\). + +When \(p\) is odd, \(y = 3(2(u - 1) + 7)\) for some \(u \in \mathds{Z}\), \(y = 6u + 15 \in (6, 9, 15)\). + +\subsection{Question Seventeen} +\label{sec:org35871b0} +\subsubsection{a} +\label{sec:orgcdd82ef} +If \(a \in I \cap J\), and \(b \in I \cap J\), then \(a \in I\), \(b \in I\), \(a \in J\), and \(b \in J\). Then, \(a - b \in I\) and \(a - b \in J\), so +\(a - b \in I \cap J\). + +If \(a \in I \cap J\) and \(r \in R\), then \(ra \in I\), \(ra \in J\), \(ar \in J\), and \(ar \in I\) by definition of I and J. + +Therefore, \(I \cap J\) is an ideal in \(R\). +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/abstract_algebra_assn_11.org b/Homework/math4310/abstract_algebra_assn_11.org new file mode 100644 index 0000000..45838e0 --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_11.org @@ -0,0 +1,118 @@ +#+TITLE: Assignment Eleven +#+AUTHOR: Lizzy Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} \usepackage{polynom} \usepackage{wasysym} +#+LATEX: \setlength\parindent{0pt} +#+OPTIONS: toc:nil + +* Section 6.1 +** Question Twenty-One +The ideal $(a) + (b)$ is generated by all linear combinations of $a$ and $b$, $x \in (a) + (b) \Rightarrow x = a c_1 + b c_2$ + +By definition, $d | a$ and $d | b$, so $a = d a_1$ and $b = d b_1$. Then, $x \in (a) + (b) \Rightarrow x = d a_1 c_1 + d b_1 c_2 = d(a_1 c_1 + b_1 c_2)$, +so $(a) + (b) \sube (c)$. + +By Theorem 1.2, $d = au + bv$ which is a linear combination of $a$ and $b$, so $d \in (a) + (b)$. Since +every multiple of $d$ is also a multiple of $a$ and $b$, $(d) \sube (a) + (b)$. + +So, $(d) = (a) + (b)$. + +* Section 6.2 +** Question Two +Let $f : F \rightarrow R$ with $R$ being the image, so the kernel of $f$ is an ideal in the field $F$ by Theorem 6.10. +Then assuming from the hint, that question ten in 6.1 is true, the only ideals in $F$ are either $(0_F)$ or $F$ +itself. So, $\text{ker}(f) = (0_F)$ or $F$. + +When $\text{ker}(f) = (0_F)$ then $f$ is injective by Theorem 6.11, and is thus an isomorphism. + +When $\text{ker}(f) = F$ then $R = \{ 0_F \}$. + +** Question Four +*** a +$f$ is consistent, as when +$[a]_{12}_{} = [b]_{12}_{}_{} (a \equiv b \text{ mod } 12 \Rightarrow a - b = 12n)$, then $[a]_4 = [b]_4$ as +$a - b \equiv 20n \text{ mod } 4 = a - b \equiv 0 \text{ mod } 4 \Rightarrow a \equiv b \text{ mod } 4$. + +*** b +The kernel of $f$ is the ideal $(4)$ as $f(x) \ni x \in (4) \Rightarrow f(x) = [4n]_{4} = [0]_4$. + +** Question Six +The kernel of \phi are polynomials in $\mathds{R}[x]$ with a root of 2. By Theorem 4.16, $x - 2$ must be a factor, so +$\text{ker}(\phi)$ is the set of all multiples of $x-2$ in $\mathds{R}[x] = (x - 2)$. + +** Question Nine +*** a +There is surjectivity as $x \in \mathds{Z}$, then the matrix $\big(\begin{smallmatrix} + x & 0\\ + 0 & 0 +\end{smallmatrix}\big)$ maps to $x$. + +It is a homomorphism since $f(x + y) = \big(\begin{smallmatrix} + a & 0\\ + c & d +\end{smallmatrix}\big) + \big(\begin{smallmatrix} + e & 0\\ + g & h +\end{smallmatrix}\big) = \big(\begin{smallmatrix} + a + e & 0 \\ + c + g & d + h +\end{smallmatrix}\big) = (a + e) = f(x) + f(y)$, +$f(xy) = \big(\begin{smallmatrix} + a & 0\\ + c & d +\end{smallmatrix}\big) \cdot \big(\begin{smallmatrix} + e & 0\\ + g & h +3\end{smallmatrix}\big) = \big(\begin{smallmatrix} + ae & 0 \\ + ce + dc & dh +\end{smallmatrix}\big) = ae = f(x)f(y)$, and the identity matrix is mapped to $1$. + +*** b +$\{ \big(\begin{smallmatrix} + 0 & 0 \\ + c & d +\end{smallmatrix}\big) | c, d \in \mathds{Z} \}$ + +** Question Ten +*** a +By definition, $x, y \in f(I) \Rightarrow \exists z, t \in I \ni f(z) = x, f(t) = b$, and $f(I)$ is also a subset of $S$. + +By hormomorphism, $f(z) - f(t) = x - y \Rightarrow f(z - t) = x - y \in I$. + +For $s \in S \Rightarrow \exists r \in R \ni f(r) = s$ by surjection. Then, $x f(r) = s x = f(z) f(r) = f(zr) \in f(I)$ + +*** b +Let $R = \mathds{R}$, $S = \mathds{C}$, and $f : R \rightarrow S \ni f(x) = x + 0i$. $f$ is not a surjective +homomorphism ($i$ has no associated element in $\mathds{R}$), and $\mathds{R}$ is an ideal in $\mathds{R}$. + +However, $f(\mathds{R})$ is not an ideal by the trivial example that +$f(1)(i) = (1 + 0i)(0 + i) = i \notin \mathds{R}$. + +** Question Seventeen +*** a +$f(a + b) = ((a + b) + I, (a + b) + J) = ((a + I) + (b + I), (a + J) + (b + J)) = (a + I, a + J) + (b + I, b + J) = f(a) + f(b)$. + +Similarly, $f(a)f(b) = f(ab)$: $f(ab) = (ab + I, ab + J)$ and $f(a)f(b) = (a + I, a + J)(b + I, b + J) = ((a + I)(b + I), (a + J)(b + J)) = (ab + I, ab + J)$. + +*** b +If we consider $R = \mathds{Z}, I = (2)$, and $J = (4)$, the elements in \mathds{Z}/(2) x \mathds{Z}/(4) are: + +{(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3)} + +There's at least one domain element that is impossible to get to: $(1, 0)$ - an integer +can't be equivalent to $1$ mod $2$ and also $0$ mod $4$. So, $f$ is not necessarily surjective. + +** Question Twenty-One +Let $f : \mathds{Z}_{20} \rightarrow \mathds{Z}_5$ such that $f([a]_{20}) = [a]_5$. $f$ is consistent because when +$[a]_{20} = [b]_{20}_{} (a \equiv b \text{ mod } 20 \Rightarrow a - b = 20n)$, then $[a]_5 = [b]_5$ as +$a - b \equiv 20n \text{ mod } 5 = a - b \equiv 0 \text{ mod } 5 \Rightarrow a \equiv b \text{ mod } 5$. + +Also, $f$ is a surjective homomorphism: ++ $f([a]_{20} + [b]_{20}) = f([a + b]_{20}) = [(a + b)]_5 = [a]_5 + [b]_5 = f([a]_{20}) + f([b]_{20})$ ++ $f([a]_{20} * [b]_{20}) = f([a * b]_{20}) = [(a * b)]_5 = [a]_5 * [b]_5 = f([a]_{20}) * f([b]_{20})$ ++ For each $[x]_5$ there exists $[y]_{20}$ such that $f([y]_{20}) = [x]_5$. The trivial solution is + that $x = y$. + +Finally, the kernel of $f$ is the ideal $(5)$ as $x \in (5) \Rightarrow f(x) = [5n]_5 = [0]_5$. Thus, +$\mathds{Z}_{20} / (5)$ is isomorphic to $\mathds{Z}_5$ by the First Isomorphism Theorem. diff --git a/Homework/math4310/abstract_algebra_assn_11.pdf b/Homework/math4310/abstract_algebra_assn_11.pdf Binary files differnew file mode 100644 index 0000000..c44c52c --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_11.pdf diff --git a/Homework/math4310/abstract_algebra_assn_11.tex b/Homework/math4310/abstract_algebra_assn_11.tex new file mode 100644 index 0000000..7ad046e --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_11.tex @@ -0,0 +1,162 @@ +% Created 2023-04-17 Mon 12:52 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} \usepackage{polynom} \usepackage{wasysym} +\author{Lizzy Hunt} +\date{\today} +\title{Assignment Eleven} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Assignment Eleven}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Section 6.1} +\label{sec:org7b8fe71} +\subsection{Question Twenty-One} +\label{sec:orga85b892} +The ideal \((a) + (b)\) is generated by all linear combinations of \(a\) and \(b\), \(x \in (a) + (b) \Rightarrow x = a c_1 + b c_2\) + +By definition, \(d | a\) and \(d | b\), so \(a = d a_1\) and \(b = d b_1\). Then, \(x \in (a) + (b) \Rightarrow x = d a_1 c_1 + d b_1 c_2 = d(a_1 c_1 + b_1 c_2)\), +so \((a) + (b) \sube (c)\). + +By Theorem 1.2, \(d = au + bv\) which is a linear combination of \(a\) and \(b\), so \(d \in (a) + (b)\). Since +every multiple of \(d\) is also a multiple of \(a\) and \(b\), \((d) \sube (a) + (b)\). + +So, \((d) = (a) + (b)\). + +\section{Section 6.2} +\label{sec:orgf462b61} +\subsection{Question Two} +\label{sec:org6ec012f} +Let \(f : F \rightarrow R\) with \(R\) being the image, so the kernel of \(f\) is an ideal in the field \(F\) by Theorem 6.10. +Then assuming from the hint, that question ten in 6.1 is true, the only ideals in \(F\) are either \((0_F)\) or \(F\) +itself. So, \(\text{ker}(f) = (0_F)\) or \(F\). + +When \(\text{ker}(f) = (0_F)\) then \(f\) is injective by Theorem 6.11, and is thus an isomorphism. + +When \(\text{ker}(f) = F\) then \(R = \{ 0_F \}\). + +\subsection{Question Four} +\label{sec:orgb116fb8} +\subsubsection{a} +\label{sec:org3bb1cfa} +\(f\) is consistent, as when +\([a]_{12}_{} = [b]_{12}_{}_{} (a \equiv b \text{ mod } 12 \Rightarrow a - b = 12n)\), then \([a]_4 = [b]_4\) as +\(a - b \equiv 20n \text{ mod } 4 = a - b \equiv 0 \text{ mod } 4 \Rightarrow a \equiv b \text{ mod } 4\). + +\subsubsection{b} +\label{sec:orgf598f8c} +The kernel of \(f\) is the ideal \((4)\) as \(f(x) \ni x \in (4) \Rightarrow f(x) = [4n]_{4} = [0]_4\). + +\subsection{Question Six} +\label{sec:org7e819f2} +The kernel of \(\phi\) are polynomials in \(\mathds{R}[x]\) with a root of 2. By Theorem 4.16, \(x - 2\) must be a factor, so +\(\text{ker}(\phi)\) is the set of all multiples of \(x-2\) in \(\mathds{R}[x] = (x - 2)\). + +\subsection{Question Nine} +\label{sec:orgff395bd} +\subsubsection{a} +\label{sec:org2a1ef62} +There is surjectivity as \(x \in \mathds{Z}\), then the matrix \(\big(\begin{smallmatrix} + x & 0\\ + 0 & 0 +\end{smallmatrix}\big)\) maps to \(x\). + +It is a homomorphism since \(f(x + y) = \big(\begin{smallmatrix} + a & 0\\ + c & d +\end{smallmatrix}\big) + \big(\begin{smallmatrix} + e & 0\\ + g & h +\end{smallmatrix}\big) = \big(\begin{smallmatrix} + a + e & 0 \\ + c + g & d + h +\end{smallmatrix}\big) = (a + e) = f(x) + f(y)\), +\(f(xy) = \big(\begin{smallmatrix} + a & 0\\ + c & d +\end{smallmatrix}\big) \cdot \big(\begin{smallmatrix} + e & 0\\ + g & h +3\end{smallmatrix}\big) = \big(\begin{smallmatrix} + ae & 0 \\ + ce + dc & dh +\end{smallmatrix}\big) = ae = f(x)f(y)\), and the identity matrix is mapped to \(1\). + +\subsubsection{b} +\label{sec:org036e3e8} +\(\{ \big(\begin{smallmatrix} + 0 & 0 \\ + c & d +\end{smallmatrix}\big) | c, d \in \mathds{Z} \}\) + +\subsection{Question Ten} +\label{sec:org3604c40} +\subsubsection{a} +\label{sec:org626043a} +By definition, \(x, y \in f(I) \Rightarrow \exists z, t \in I \ni f(z) = x, f(t) = b\), and \(f(I)\) is also a subset of \(S\). + +By hormomorphism, \(f(z) - f(t) = x - y \Rightarrow f(z - t) = x - y \in I\). + +For \(s \in S \Rightarrow \exists r \in R \ni f(r) = s\) by surjection. Then, \(x f(r) = s x = f(z) f(r) = f(zr) \in f(I)\) + +\subsubsection{b} +\label{sec:org2946823} +Let \(R = \mathds{R}\), \(S = \mathds{C}\), and \(f : R \rightarrow S \ni f(x) = x + 0i\). \(f\) is not a surjective +homomorphism (\(i\) has no associated element in \(\mathds{R}\)), and \(\mathds{R}\) is an ideal in \(\mathds{R}\). + +However, \(f(\mathds{R})\) is not an ideal by the trivial example that +\(f(1)(i) = (1 + 0i)(0 + i) = i \notin \mathds{R}\). + +\subsection{Question Seventeen} +\label{sec:orgb24a5cb} +\subsubsection{a} +\label{sec:org15e7223} +\(f(a + b) = ((a + b) + I, (a + b) + J) = ((a + I) + (b + I), (a + J) + (b + J)) = (a + I, a + J) + (b + I, b + J) = f(a) + f(b)\). + +Similarly, \(f(a)f(b) = f(ab)\): \(f(ab) = (ab + I, ab + J)\) and \(f(a)f(b) = (a + I, a + J)(b + I, b + J) = ((a + I)(b + I), (a + J)(b + J)) = (ab + I, ab + J)\). + +\subsubsection{b} +\label{sec:org2bba32c} +If we consider \(R = \mathds{Z}, I = (2)\), and \(J = (4)\), the elements in \mathds{Z}/(2) x \mathds{Z}/(4) are: + +\{(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3)\} + +There's at least one domain element that is impossible to get to: \((1, 0)\) - an integer +can't be equivalent to \(1\) mod \(2\) and also \(0\) mod \(4\). So, \(f\) is not necessarily surjective. + +\subsection{Question Twenty-One} +\label{sec:org567c5e4} +Let \(f : \mathds{Z}_{20} \rightarrow \mathds{Z}_5\) such that \(f([a]_{20}) = [a]_5\). \(f\) is consistent because when +\([a]_{20} = [b]_{20}_{} (a \equiv b \text{ mod } 20 \Rightarrow a - b = 20n)\), then \([a]_5 = [b]_5\) as +\(a - b \equiv 20n \text{ mod } 5 = a - b \equiv 0 \text{ mod } 5 \Rightarrow a \equiv b \text{ mod } 5\). + +Also, \(f\) is a surjective homomorphism: +\begin{itemize} +\item \(f([a]_{20} + [b]_{20}) = f([a + b]_{20}) = [(a + b)]_5 = [a]_5 + [b]_5 = f([a]_{20}) + f([b]_{20})\) +\item \(f([a]_{20} * [b]_{20}) = f([a * b]_{20}) = [(a * b)]_5 = [a]_5 * [b]_5 = f([a]_{20}) * f([b]_{20})\) +\item For each \([x]_5\) there exists \([y]_{20}\) such that \(f([y]_{20}) = [x]_5\). The trivial solution is +that \(x = y\). +\end{itemize} + +Finally, the kernel of \(f\) is the ideal \((5)\) as \(x \in (5) \Rightarrow f(x) = [5n]_5 = [0]_5\). Thus, +\(\mathds{Z}_{20} / (5)\) is isomorphic to \(\mathds{Z}_5\) by the First Isomorphism Theorem. +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/abstract_algebra_assn_12.org b/Homework/math4310/abstract_algebra_assn_12.org new file mode 100644 index 0000000..6102c0a --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_12.org @@ -0,0 +1,26 @@ +#+TITLE: Assignment Twelve +#+AUTHOR: Lizzy Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} \usepackage{polynom} \usepackage{wasysym} +#+LATEX: \setlength\parindent{0pt} +#+OPTIONS: toc:nil + +* Section 6.3 +** Question One +$n = cd$ with some $1 < |c| < |n|$ and $1 < |d| < |n|$ since $n$ is composite, so $c$ and $d$ are not multiples of $n$. Therefore as $cd \in (n)$ but $c \notin (n)$ and $d \notin (n)$ then $(n)$ is not a prime ideal +by definition. + +** Question Five +Both $\mathds{Z}_6$ and $\mathds{Z}_{12}$'s maximal ideals are $(2)$ and $(3) +** Question Six +*** a +The only maximal ideal of $\mathds{Z}_8$ is $(2)$ since it is its prime divisor. + +Similarly, the only maximal ideal of $\mathds{Z}_9$ is $(3)$. + +*** b +In $\mathds{Z}_{10}$ the maximal ideals are $(2)$ and $(5)$, similarly for $\mathds{Z}_{15}$: $(3)$ and $(5)$. + +** Question Eight +Consider $(2) \cap (3)$ which generates $(6)$, and is not prime in $\mathds{Z}$; $3 \cdot 2 \in (6)$ but $3 \notin (6)$ and $2 \notin (6)$. + diff --git a/Homework/math4310/abstract_algebra_assn_12.pdf b/Homework/math4310/abstract_algebra_assn_12.pdf Binary files differnew file mode 100644 index 0000000..1a6b5c8 --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_12.pdf diff --git a/Homework/math4310/abstract_algebra_assn_12.tex b/Homework/math4310/abstract_algebra_assn_12.tex new file mode 100644 index 0000000..0e39503 --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_12.tex @@ -0,0 +1,56 @@ +% Created 2023-04-23 Sun 13:45 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} \usepackage{polynom} \usepackage{wasysym} +\author{Lizzy Hunt} +\date{\today} +\title{Assignment Twelve} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Assignment Twelve}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Section 6.3} +\label{sec:org86da123} +\subsection{Question One} +\label{sec:org600275c} +\(n = cd\) with some \(1 < |c| < |n|\) and \(1 < |d| < |n|\) since \(n\) is composite, so \(c\) and \(d\) are not multiples of \(n\). Therefore as \(cd \in (n)\) but \(c \notin (n)\) and \(d \notin (n)\) then \((n)\) is not a prime ideal +by definition. + +\subsection{Question Five} +\label{sec:org37fce42} +Both \(\mathds{Z}_6\) and \(\mathds{Z}_{12}\)'s maximal ideals are \((2)\) and \$(3) +\subsection{Question Six} +\label{sec:org18d9056} +\subsubsection{a} +\label{sec:org0890b14} +The only maximal ideal of \(\mathds{Z}_8\) is \((2)\) since it is its prime divisor. + +Similarly, the only maximal ideal of \(\mathds{Z}_9\) is \((3)\). + +\subsubsection{b} +\label{sec:org77d60ec} +In \(\mathds{Z}_{10}\) the maximal ideals are \((2)\) and \((5)\), similarly for \(\mathds{Z}_{15}\): \((3)\) and \((5)\). + +\subsection{Question Eight} +\label{sec:org38c7c8c} +Consider \((2) \cap (3)\) which generates \((6)\), and is not prime in \(\mathds{Z}\); \(3 \cdot 2 \in (6)\) but \(3 \notin (6)\) and \(2 \notin (6)\). +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/abstract_algebra_assn_9.org b/Homework/math4310/abstract_algebra_assn_9.org new file mode 100644 index 0000000..41fb8a0 --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_9.org @@ -0,0 +1,229 @@ +#+TITLE: Assignment Nine +#+AUTHOR: Lizzy Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,landscape]{geometry} \usepackage{polynom} \usepackage{wasysym} +#+LATEX: \setlength\parindent{0pt} +#+OPTIONS: toc:nil + +* Section 5.1 +** Question One +*** b +Yes. In $F$, $f(x) - g(x) = -x^3 + x = x^3 + x$. + +\begin{equation*} +\polylongdiv[style=A]{x^3 + x}{x^2+1} +\end{equation*} + +*** c +No. $f(x) - g(x) = x^5 - 2x^4 + 4x^3 - 8x^2 + 3x - 2$ + +\begin{equation*} +\polylongdiv[style=A]{x^5 - 2x^4 + 4x^3 - 8x^2 + 3x - 2}{x^3 - x^2 + x - 1} +\end{equation*} + +** Question Three +$|${ $0, 1, x, x + 1, x^2, x^2 + 1, x^2 + x, x^2 + x + 1$ }$|$ = 8 + +** Question Four +For every $a,b,c \in \mathds{Z}_3$ we can generate a polynomial $ax^2 + bx + c$, by part two of Corollary 5.5. $3^3 = 27$ + +** Question Six +By Corollary 5.5, all the congruence classes in $F[x]$ are $c \ni c \in F$. + +** Question Eight +\begin{align*} +f(x)k(x) &\equiv_{p(x)} g(x)k(x) \\ +& \Rightarrow p(x) | f(x)k(x) - g(x)k(x) \\ +& \Rightarrow p(x) | (f(x) - g(x))(k(x)) +\end{align*} + +By Theorem 4.10, since $p(x)$ is relatively prime to $k(x)$, $p(x) | f(x) - g(x) \Rightarrow f(x) \equiv_{p(x)} g(x)$ + +** Question Eleven +Since $p(x)$ is reducible, it can be rewritten as $p(x) = f(x)g(x)$ with $f(x), g(x) \in F[x]$ with each $f(x)$ and $g(x)$ having a degree greater than 0, summing to the +degree of $p(x)$. + +Then, it is impossible for $p(x)$ to divide $f(x)$ or $g(x)$ since $p(x)$ has a higher degree. So, neither $f(x)$ or $g(x)$ can $ \equiv_{p(x)} 0_F$. + +Still, $f(x)g(x) \equiv_{}_{p(x)} p(x) \equiv_{p(x)} 0_F$ since $p(x) | p(x)$. + +* Section 5.2 +** Question One +The congruence classes are those in Section 5.1, Question Three as above. + +| + | [0] | [1] | [x] | [x + 1] | [x^2] | [x^2 + 1] | [x^2 + x] | [x^2 + x + 1] | +| [0] | [0] | [1] | [x] | [x + 1] | [x^2] | [x^2 + 1] | [x^2 + x] | [x^2 + x + 1] | +| [1] | [1] | [0] | [x+1] | [x] | [x^2 + 1] | [x^2] | [x^2 + x + 1] | [x^2 + x] | +| [x] | [x] | [x + 1] | [0] | [1] | [x^2 + x] | [x^2 + x + 1] | [x^2] | [x^2 + 1] | +| [x + 1] | [x + 1] | [x] | [1] | [0] | [x^2 + x + 1] | [x^2 + x] | [x^2 + 1] | [x^2] | +| [x^2] | [x^2] | [x^2 + 1] | [x^2 + x] | [x^2 + x + 1] | [0] | [1] | [x] | [x + 1] | +| [x^2 + 1] | [x^2 + 1] | [x^2] | [x^2 + x + 1] | [x^2 + x] | [1] | [0] | [x + 1] | [x] | +| [x^2 + x] | [x^2 + x] | [x^2 + x + 1] | [x^2] | [x^2 + 1] | [x] | [x+1] | [0] | [1] | +| [x^2 + x + 1] | [x^2 + x + 1] | [x^2 + x] | [x^2 + 1] | [x^2] | [x+1] | [x] | [1] | [0] | + +| \cdot | [0] | [1] | [x] | [x + 1] | [x^2] | [x^2 + 1] | [x^2 + x] | [x^2 + x + 1] | +| [0] | [0] | [0] | [0] | [0] | [0] | [0] | [0] | [0] | +| [1] | [0] | [1] | [x] | [x + 1] | [x^2] | [x^2 + 1] | [x^2 + x] | [x^2 + x + 1] | +| [x] | [0] | [x] | [x^2] | [x^2+x] | [x+1] | [1] | [x^2+x+1] | [x^2+1] | +| [x + 1] | [0] | [x + 1] | [x^2 + x] | [x^2+1] | [x^2+x+1] | [x^2] | [1] | [x] | +| [x^2] | [0] | [x^2] | [x+1] | [x^2+x+1] | [x^2+x] | [x] | [x^2+1] | [1] | +| [x^2 + 1] | [0] | [x^2 + 1] | [1] | [x^2] | [x] | [x^2+x+1] | [x+1] | [x^2+x] | +| [x^2 + x] | [0] | [x^2 + x] | [x^2+x+1] | [1] | [x^2+1] | [x+1] | [x] | [x+1] | +| [x^2 + x + 1] | [0] | [x^2 + x + 1] | [x^2+1] | [x] | [1] | [x^2+x] | [x^2] | [x+1] | + +Yes, this is a field since by Theorem 5.7, it is a commutative ring with identity, and each +non-zero row in the multiplication table contains the multiplicative identity (each is a unit). + +** Question Two +| + | [0] | [1] | [2] | [x] | [x+1] | [x+2] | [2x] | [2x+1] | [2x+2] | +| [0] | [0] | [1] | [2] | [x] | [x+1] | [x+2] | [2x] | [2x+1] | [2x+2] | +| [1] | [1] | [2] | [0] | [x+1] | [x+2] | [x] | [2x+1] | [2x+2] | [2x] | +| [2] | [2] | [0] | [1] | [x+2] | [x] | [x+1] | [2x+2] | [2x] | [2x+1] | +| [x] | [x] | [x+1] | [x+2] | [2x] | [2x+1] | [2x+2] | [0] | [1] | [2] | +| [x+1] | [x+1] | [x+2] | [x] | [2x+1] | [2x+2] | [2x] | [1] | [2] | [0] | +| [x+2] | [x+2] | [x] | [x+1] | [2x+2] | [2x] | [2x+1] | [2] | [0] | [1] | +| [2x] | [2x] | [2x+1] | [2x+2] | [0] | [1] | [2] | [x] | [x+1] | [1] | +| [2x+1] | [2x+1] | [2x+2] | [2x] | [1] | [2] | [0] | [x+1] | [x+2] | [x] | +| [2x+2] | [2x+2] | [2x] | [2x+1] | [2] | [0] | [1] | [x+2] | [x] | [x+1] | + + +| \cdot | [0] | [1] | [2] | [x] | [x+1] | [x+2] | [2x] | [2x+1] | [2x+2] | +| [0] | [0] | [0] | [0] | [0] | [0] | [0] | [0] | [0] | [0] | +| [1] | [0] | [1] | [2] | [x] | [x+1] | [x+2] | [2x] | [2x+1] | [2x+2] | +| [2] | [0] | [2] | [1] | [2x] | [2x+2] | [2x+1] | [x] | [x+2] | [x+1] | +| [x] | [0] | [x] | [2x] | [2] | [x+2] | [2x+2] | [1] | [x+1] | [2x+1] | +| [x+1] | [0] | [x+1] | [2x+2] | [x+2] | [2x] | [1] | [2x+1] | [2] | [x] | +| [x+2] | [0] | [x+2] | [2x+1] | [2x+2] | [1] | [x] | [x+1] | [2x] | [2] | +| [2x] | [0] | [2x] | [x] | [1] | [2x+1] | [x+1] | [2] | [2x+2] | [x+2] | +| [2x+1] | [0] | [2x+1] | [x+2] | [x+1] | [2] | [2x] | [2x+2] | [x] | [1] | +| [2x+2] | [0] | [2x+2] | [x+1] | [2x+1] | [x] | [2] | [x+2] | [1] | [2x] | + +Yes, this is a field since by Theorem 5.7, it is a commutative ring with identity, and each +non-zero row in the multiplication table contains the multiplicative identity (each is a unit). + +** Question Three + +| + | [0] | [1] | [x] | [x+1] | +| [0] | [0] | [1] | [x] | [x+1] | +| [1] | [1] | [0] | [x+1] | [x] | +| [x] | [x] | [x+1] | [0] | [1] | +| [x+1] | [x+1] | [x] | [1] | [0] | + +| \cdot | [0] | [1] | [x] | [x+1] | +| [0] | [0] | [0] | [0] | [0] | +| [1] | [0] | [1] | [x] | [x+1] | +| [x] | [0] | [x] | [1] | [x+1] | +| [x+1] | [0] | [x+1] | [x+1] | [0] | + +Not, this is _not_ a field since by Theorem 5.7, it is a commutative ring with identity, but +not every non-zero row in the multiplication table contains the multiplicative identity ($x+1$ is +not a unit). + +** Question Six +By Corollary 5.5, each congruence class can be rewritten with $a,b \in \mathds{Q}$: $[ax + b]$. + +Addition is defined as $[ax + b] + [cx + d] = [(a + c)x + bd]$. + +$(ax + b)(cx + d) = acx^2 + dax + bcx + bd = acx^2 + (da + bc)x + bd$ + +\begin{equation*} +\polylongdiv[style=A]{acx^2 + (da + bc)x + bd}{x^2 - 2} +\end{equation*} + +Multiplication is thusly defined as $[ax + b] \cdot [cx + d] = [(ad + bc)x + (2ac + bd)]$ + +** Question Nine +Given that $[a + bx]$ is a nonzero congruence class, either +$a > 0$ or $b > 0$. Then let $c = \frac{-a}{a^2 + b^2}$ and $d = \frac{b}{a^2 + b^2}$. + +\begin{equation*} +\polylongdiv[style=A]{acx^2 + (da + bc)x + bd}{x^2 + 1} +\end{equation*} + +\begin{align*} +[ax + b][cx + d] & = [(ad + bc)x + (bd - ac)] \\ +&= [(\frac{ab}{a^2 + b^2} + \frac{-ab}{a^2 + b^2})x + \frac{b^2}{a^2 + b^2} - \frac{-a^2}{a^2 + b^2}] \\ +&= [0x + \frac{b^2 + a^2}{a^2 + b^2}] \\ +&= [1] +\end{align*} + +* Section 5.3 +** Question One +*** a +$x^3 + 2x^2 + x + 1$ does not have any roots in \mathds{Z}_3, so by Corollary 4.19 it must be irreducible, +and thus a field by 5.10 + +*** b +This is not a field by Theorem 5.10 since 2 is a root in $Z_5$, so by Corollary 4.19 it must be reducible. + +*** c +This is not a field by Theorem 5.10 since $x^4 + x^2 + 1 = (x^2 - x + 1)(x^2 + x + 1) \equiv_2 (x^2 + x + 1)^2$ shows $x^4 + x^2 + 1$ is reducible. + +** Question Two +*** a +Since $\mathds{Q} (\sqrt{2})$ is a subset of $\mathds{R}$, multiplication and addition are associative, commutative, and distributive. + +The additive identity of $\mathds{Q} (\sqrt{2}) is $0 + 0\sqrt{2}$ and the multiplicative identity is $1 + 0\sqrt{2}$. + +It must be a field since every non-zero element $a + b \sqrt{2}$ is a unit: + +\begin{align*} +(a + b\sqrt{2})x = 1 & \Rightarrow x = \frac{1}{a + b\sqrt{2}} \\ +& \Rightarrow x = \frac{a - b\sqrt{2}}{(a + b\sqrt{2})(a - b \sqrt{2})} \\ +& \Rightarrow x = \frac{a}{a^2 - 2b^2} - \frac{b}{a^2 - 2b^2}\sqrt{2} \\ +\end{align*} + +*** b +Every element in $\mathds{Q} / (x^2 - 2)$ can be rewritten as a member of the congruence class $[ax + b]$ with $a, b \in \mathds{Q}$ by Corollary 5.5. + +Then, we can define a function $f$ such that $f([ax + b]) = a + b\sqrt{2}$ so that $f(x) \in \mathds{Q}(\sqrt{2})$. + +$f$ is thus an isomorphism since (a chance at redemption from my midterm \smiley): + ++ $f$ is injective since $f([ax + b]) = f([cx + d]) \Rightarrow a + b\sqrt{2} = c + d\sqrt{2} \Rightarrow a = c \wedge b = d$ ++ $f$ is surjective since each $a + b\sqrt{2}$ is uniquely mapped to $[ax + b]$ ++ $f([ax + b] + [cx + d]) = f([(a + c)x + (b + d)]) = (a + c) + (b + d)\sqrt{2} = (a + b\sqrt{2}) + (c + d\sqrt{2}) = f([ax + b]) + f([cx + d])$ + ++ And via Question Six from section 5.2 above, + $f([ax + b] \cdot [cx + d]) = f([(ad + bc)x + (2ac + bd)]) = (ad + bc) + (2ac + bd)\sqrt{2} = (a + b\sqrt{2})(c + d\sqrt{2}) = f([ax + b])f([cx + d])$ + +** Question Five +*** a +Since $\mathds{Q} (\sqrt{3})$ is a subset of $\mathds{R}$, multiplication and addition are associative, commutative, and distributive. + +The additive identity of $\mathds{Q} (\sqrt{3}) is $0 + 0\sqrt{3}$ and the multiplicative identity is $1 + 0\sqrt{3}$. + +It must be a field since every non-zero element $r + s \sqrt{3}$ is a unit (by first assuming that the inverse of $r + s\sqrt{3}$ from the +back of the book, is $\frac{r}{t} - \frac{s}{t}\sqrt{3}$ with $t=r^2 - 3s^2$): + +\begin{align*} +1 &= (r + s\sqrt{3})(\frac{r}{t} - \frac{s}{t}\sqrt{3}) \\ + &= \frac{r^2}{t} - \frac{sr}{t}\sqrt{3} + \frac{sr}{t}\sqrt{3} - \frac{3s^2}{t} \\ + &= \frac{r^2 - 3s^2}{t} \\ + &= 1 +\end{align*} + +*** b +**** Quick Lemma +In $\mathds{Q}{x^2 - 3}$, by Corollary 5.5, each congruence class can be rewritten with $a,b \in \mathds{Q}$: $[ax + b]$. + +$(ax + b)(cx + d) = acx^2 + dax + bcx + bd = acx^2 + (da + bc)x + bd$ + +\begin{equation*} +\polylongdiv[style=A]{acx^2 + (da + bc)x + bd}{x^2 - 3} +\end{equation*} + +Multiplication is thusly defined as $[ax + b] \cdot [cx + d] = [(ad + bc)x + (3ac + bd)]$ + +**** Yeah, it's an isomorphism + +Every element in $\mathds{Q} / (x^2 - 3)$ can be rewritten as a member of the congruence class $[ax + b]$ with $a, b \in \mathds{Q}$ by Corollary 5.5. + +Then, we can define a function $f$ such that $f([rx + s]) = r + s\sqrt{3}$ so that $f(x) \in \mathds{Q}(\sqrt{3})$. + +$f$ is thus an isomorphism since (a chance of redemption from my midterm \smiley): + ++ $f$ is injective since $f([ax + b]) = f([cx + d]) \Rightarrow a + b\sqrt{3} = c + d\sqrt{3} \Rightarrow a = c \wedge b = d$ ++ $f$ is surjective since each $a + b\sqrt{3}$ is uniquely mapped to $[ax + b]$ ++ $f([ax + b] + [cx + d]) = f([(a + c)x + (b + d)]) = (a + c) + (b + d)\sqrt{3} = (a + b\sqrt{3}) + (c + d\sqrt{3}) = f([ax + b]) + f([cx + d])$ ++ And from the lemma, $f([ax + b] \cdot [cx + d]) = f([(ad + bc)x + (3ac + bd)]) = (ad + bc) + (3ac + bd)\sqrt{3} = (a + b\sqrt{3})(c + d\sqrt{3}) = f([ax + b])f([cx + d])$ diff --git a/Homework/math4310/abstract_algebra_assn_9.pdf b/Homework/math4310/abstract_algebra_assn_9.pdf Binary files differnew file mode 100644 index 0000000..6b8bd78 --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_9.pdf diff --git a/Homework/math4310/abstract_algebra_assn_9.tex b/Homework/math4310/abstract_algebra_assn_9.tex new file mode 100644 index 0000000..8f7b752 --- /dev/null +++ b/Homework/math4310/abstract_algebra_assn_9.tex @@ -0,0 +1,311 @@ +% Created 2023-03-27 Mon 22:00 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,landscape]{geometry} \usepackage{polynom} \usepackage{wasysym} +\author{Lizzy Hunt} +\date{\today} +\title{Assignment Nine} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Assignment Nine}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Section 5.1} +\label{sec:orga03a7b4} +\subsection{Question One} +\label{sec:org41cc8bf} +\subsubsection{b} +\label{sec:org39f646c} +Yes. In \(F\), \(f(x) - g(x) = -x^3 + x = x^3 + x\). + +\begin{equation*} +\polylongdiv[style=A]{x^3 + x}{x^2+1} +\end{equation*} + +\subsubsection{c} +\label{sec:orge019c41} +No. \(f(x) - g(x) = x^5 - 2x^4 + 4x^3 - 8x^2 + 3x - 2\) + +\begin{equation*} +\polylongdiv[style=A]{x^5 - 2x^4 + 4x^3 - 8x^2 + 3x - 2}{x^3 - x^2 + x - 1} +\end{equation*} + +\subsection{Question Three} +\label{sec:org1718036} +\(|\)\{ \(0, 1, x, x + 1, x^2, x^2 + 1, x^2 + x, x^2 + x + 1\) \}\(|\) = 8 + +\subsection{Question Four} +\label{sec:orgd724559} +For every \(a,b,c \in \mathds{Z}_3\) we can generate a polynomial \(ax^2 + bx + c\), by part two of Corollary 5.5. \(3^3 = 27\) + +\subsection{Question Six} +\label{sec:orgb081ff5} +By Corollary 5.5, all the congruence classes in \(F[x]\) are \(c \ni c \in F\). + +\subsection{Question Eight} +\label{sec:org4c8f836} +\begin{align*} +f(x)k(x) &\equiv_{p(x)} g(x)k(x) \\ +& \Rightarrow p(x) | f(x)k(x) - g(x)k(x) \\ +& \Rightarrow p(x) | (f(x) - g(x))(k(x)) +\end{align*} + +By Theorem 4.10, since \(p(x)\) is relatively prime to \(k(x)\), \(p(x) | f(x) - g(x) \Rightarrow f(x) \equiv_{p(x)} g(x)\) + +\subsection{Question Eleven} +\label{sec:org98dcd2c} +Since \(p(x)\) is reducible, it can be rewritten as \(p(x) = f(x)g(x)\) with \(f(x), g(x) \in F[x]\) with each \(f(x)\) and \(g(x)\) having a degree greater than 0, summing to the +degree of \(p(x)\). + +Then, it is impossible for \(p(x)\) to divide \(f(x)\) or \(g(x)\) since \(p(x)\) has a higher degree. So, neither \(f(x)\) or \(g(x)\) can \$ \(\equiv\)\textsubscript{p(x)} 0\textsubscript{F}\$. + +Still, \(f(x)g(x) \equiv_{}_{p(x)} p(x) \equiv_{p(x)} 0_F\) since \(p(x) | p(x)\). + +\section{Section 5.2} +\label{sec:org9a01661} +\subsection{Question One} +\label{sec:org8ab076f} +The congruence classes are those in Section 5.1, Question Three as above. + +\begin{center} +\begin{tabular}{lllllllll} ++ & [0] & [1] & [x] & [x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1]\\[0pt] +[0] & [0] & [1] & [x] & [x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1]\\[0pt] +[1] & [1] & [0] & [x+1] & [x] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2} + x]\\[0pt] +[x] & [x] & [x + 1] & [0] & [1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1]\\[0pt] +[x + 1] & [x + 1] & [x] & [1] & [0] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2}]\\[0pt] +[x\textsuperscript{2}] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1] & [0] & [1] & [x] & [x + 1]\\[0pt] +[x\textsuperscript{2} + 1] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2} + x] & [1] & [0] & [x + 1] & [x]\\[0pt] +[x\textsuperscript{2} + x] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x] & [x+1] & [0] & [1]\\[0pt] +[x\textsuperscript{2} + x + 1] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2}] & [x+1] & [x] & [1] & [0]\\[0pt] +\end{tabular} +\end{center} + +\begin{center} +\begin{tabular}{lllllllll} +\(\cdot\) & [0] & [1] & [x] & [x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1]\\[0pt] +[0] & [0] & [0] & [0] & [0] & [0] & [0] & [0] & [0]\\[0pt] +[1] & [0] & [1] & [x] & [x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1]\\[0pt] +[x] & [0] & [x] & [x\textsuperscript{2}] & [x\textsuperscript{2}+x] & [x+1] & [1] & [x\textsuperscript{2}+x+1] & [x\textsuperscript{2}+1]\\[0pt] +[x + 1] & [0] & [x + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2}+1] & [x\textsuperscript{2}+x+1] & [x\textsuperscript{2}] & [1] & [x]\\[0pt] +[x\textsuperscript{2}] & [0] & [x\textsuperscript{2}] & [x+1] & [x\textsuperscript{2}+x+1] & [x\textsuperscript{2}+x] & [x] & [x\textsuperscript{2}+1] & [1]\\[0pt] +[x\textsuperscript{2} + 1] & [0] & [x\textsuperscript{2} + 1] & [1] & [x\textsuperscript{2}] & [x] & [x\textsuperscript{2}+x+1] & [x+1] & [x\textsuperscript{2}+x]\\[0pt] +[x\textsuperscript{2} + x] & [0] & [x\textsuperscript{2} + x] & [x\textsuperscript{2}+x+1] & [1] & [x\textsuperscript{2}+1] & [x+1] & [x] & [x+1]\\[0pt] +[x\textsuperscript{2} + x + 1] & [0] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2}+1] & [x] & [1] & [x\textsuperscript{2}+x] & [x\textsuperscript{2}] & [x+1]\\[0pt] +\end{tabular} +\end{center} + +Yes, this is a field since by Theorem 5.7, it is a commutative ring with identity, and each +non-zero row in the multiplication table contains the multiplicative identity (each is a unit). + +\subsection{Question Two} +\label{sec:org9db49ef} +\begin{center} +\begin{tabular}{llllllllll} ++ & [0] & [1] & [2] & [x] & [x+1] & [x+2] & [2x] & [2x+1] & [2x+2]\\[0pt] +[0] & [0] & [1] & [2] & [x] & [x+1] & [x+2] & [2x] & [2x+1] & [2x+2]\\[0pt] +[1] & [1] & [2] & [0] & [x+1] & [x+2] & [x] & [2x+1] & [2x+2] & [2x]\\[0pt] +[2] & [2] & [0] & [1] & [x+2] & [x] & [x+1] & [2x+2] & [2x] & [2x+1]\\[0pt] +[x] & [x] & [x+1] & [x+2] & [2x] & [2x+1] & [2x+2] & [0] & [1] & [2]\\[0pt] +[x+1] & [x+1] & [x+2] & [x] & [2x+1] & [2x+2] & [2x] & [1] & [2] & [0]\\[0pt] +[x+2] & [x+2] & [x] & [x+1] & [2x+2] & [2x] & [2x+1] & [2] & [0] & [1]\\[0pt] +[2x] & [2x] & [2x+1] & [2x+2] & [0] & [1] & [2] & [x] & [x+1] & [1]\\[0pt] +[2x+1] & [2x+1] & [2x+2] & [2x] & [1] & [2] & [0] & [x+1] & [x+2] & [x]\\[0pt] +[2x+2] & [2x+2] & [2x] & [2x+1] & [2] & [0] & [1] & [x+2] & [x] & [x+1]\\[0pt] +\end{tabular} +\end{center} + + +\begin{center} +\begin{tabular}{llllllllll} +\(\cdot\) & [0] & [1] & [2] & [x] & [x+1] & [x+2] & [2x] & [2x+1] & [2x+2]\\[0pt] +[0] & [0] & [0] & [0] & [0] & [0] & [0] & [0] & [0] & [0]\\[0pt] +[1] & [0] & [1] & [2] & [x] & [x+1] & [x+2] & [2x] & [2x+1] & [2x+2]\\[0pt] +[2] & [0] & [2] & [1] & [2x] & [2x+2] & [2x+1] & [x] & [x+2] & [x+1]\\[0pt] +[x] & [0] & [x] & [2x] & [2] & [x+2] & [2x+2] & [1] & [x+1] & [2x+1]\\[0pt] +[x+1] & [0] & [x+1] & [2x+2] & [x+2] & [2x] & [1] & [2x+1] & [2] & [x]\\[0pt] +[x+2] & [0] & [x+2] & [2x+1] & [2x+2] & [1] & [x] & [x+1] & [2x] & [2]\\[0pt] +[2x] & [0] & [2x] & [x] & [1] & [2x+1] & [x+1] & [2] & [2x+2] & [x+2]\\[0pt] +[2x+1] & [0] & [2x+1] & [x+2] & [x+1] & [2] & [2x] & [2x+2] & [x] & [1]\\[0pt] +[2x+2] & [0] & [2x+2] & [x+1] & [2x+1] & [x] & [2] & [x+2] & [1] & [2x]\\[0pt] +\end{tabular} +\end{center} + +Yes, this is a field since by Theorem 5.7, it is a commutative ring with identity, and each +non-zero row in the multiplication table contains the multiplicative identity (each is a unit). + +\subsection{Question Three} +\label{sec:orgc80a66e} + +\begin{center} +\begin{tabular}{lllll} ++ & [0] & [1] & [x] & [x+1]\\[0pt] +[0] & [0] & [1] & [x] & [x+1]\\[0pt] +[1] & [1] & [0] & [x+1] & [x]\\[0pt] +[x] & [x] & [x+1] & [0] & [1]\\[0pt] +[x+1] & [x+1] & [x] & [1] & [0]\\[0pt] +\end{tabular} +\end{center} + +\begin{center} +\begin{tabular}{lllll} +\(\cdot\) & [0] & [1] & [x] & [x+1]\\[0pt] +[0] & [0] & [0] & [0] & [0]\\[0pt] +[1] & [0] & [1] & [x] & [x+1]\\[0pt] +[x] & [0] & [x] & [1] & [x+1]\\[0pt] +[x+1] & [0] & [x+1] & [x+1] & [0]\\[0pt] +\end{tabular} +\end{center} + +Not, this is \uline{not} a field since by Theorem 5.7, it is a commutative ring with identity, but +not every non-zero row in the multiplication table contains the multiplicative identity (\(x+1\) is +not a unit). + +\subsection{Question Six} +\label{sec:orga040020} +By Corollary 5.5, each congruence class can be rewritten with \(a,b \in \mathds{Q}\): \([ax + b]\). + +Addition is defined as \([ax + b] + [cx + d] = [(a + c)x + bd]\). + +\((ax + b)(cx + d) = acx^2 + dax + bcx + bd = acx^2 + (da + bc)x + bd\) + +\begin{equation*} +\polylongdiv[style=A]{acx^2 + (da + bc)x + bd}{x^2 - 2} +\end{equation*} + +Multiplication is thusly defined as \([ax + b] \cdot [cx + d] = [(ad + bc)x + (2ac + bd)]\) + +\subsection{Question Nine} +\label{sec:org3bd28c4} +Given that \([a + bx]\) is a nonzero congruence class, either +\(a > 0\) or \(b > 0\). Then let \(c = \frac{-a}{a^2 + b^2}\) and \(d = \frac{b}{a^2 + b^2}\). + +\begin{equation*} +\polylongdiv[style=A]{acx^2 + (da + bc)x + bd}{x^2 + 1} +\end{equation*} + +\begin{align*} +[ax + b][cx + d] & = [(ad + bc)x + (bd - ac)] \\ +&= [(\frac{ab}{a^2 + b^2} + \frac{-ab}{a^2 + b^2})x + \frac{b^2}{a^2 + b^2} - \frac{-a^2}{a^2 + b^2}] \\ +&= [0x + \frac{b^2 + a^2}{a^2 + b^2}] \\ +&= [1] +\end{align*} + +\section{Section 5.3} +\label{sec:org6b8ca6a} +\subsection{Question One} +\label{sec:org09f321d} +\subsubsection{a} +\label{sec:org00adeb0} +\(x^3 + 2x^2 + x + 1\) does not have any roots in \mathds{Z}\textsubscript{3}, so by Corollary 4.19 it must be irreducible, +and thus a field by 5.10 + +\subsubsection{b} +\label{sec:orge4a6bab} +This is not a field by Theorem 5.10 since 2 is a root in \(Z_5\), so by Corollary 4.19 it must be reducible. + +\subsubsection{c} +\label{sec:org1cc5f89} +This is not a field by Theorem 5.10 since \(x^4 + x^2 + 1 = (x^2 - x + 1)(x^2 + x + 1) \equiv_2 (x^2 + x + 1)^2\) shows \(x^4 + x^2 + 1\) is reducible. + +\subsection{Question Two} +\label{sec:org1cd3926} +\subsubsection{a} +\label{sec:org265177d} +Since \(\mathds{Q} (\sqrt{2})\) is a subset of \(\mathds{R}\), multiplication and addition are associative, commutative, and distributive. + +The additive identity of \$\mathds{Q} (\sqrt{2}) is \(0 + 0\sqrt{2}\) and the multiplicative identity is \(1 + 0\sqrt{2}\). + +It must be a field since every non-zero element \(a + b \sqrt{2}\) is a unit: + +\begin{align*} +(a + b\sqrt{2})x = 1 & \Rightarrow x = \frac{1}{a + b\sqrt{2}} \\ +& \Rightarrow x = \frac{a - b\sqrt{2}}{(a + b\sqrt{2})(a - b \sqrt{2})} \\ +& \Rightarrow x = \frac{a}{a^2 - 2b^2} - \frac{b}{a^2 - 2b^2}\sqrt{2} \\ +\end{align*} + +\subsubsection{b} +\label{sec:orgef6853e} +Every element in \(\mathds{Q} / (x^2 - 2)\) can be rewritten as a member of the congruence class \([ax + b]\) with \(a, b \in \mathds{Q}\) by Corollary 5.5. + +Then, we can define a function \(f\) such that \(f([ax + b]) = a + b\sqrt{2}\) so that \(f(x) \in \mathds{Q}(\sqrt{2})\). + +\(f\) is thus an isomorphism since (a chance at redemption from my midterm \(\ddot\smile\)): + +\begin{itemize} +\item \(f\) is injective since \(f([ax + b]) = f([cx + d]) \Rightarrow a + b\sqrt{2} = c + d\sqrt{2} \Rightarrow a = c \wedge b = d\) +\item \(f\) is surjective since each \(a + b\sqrt{2}\) is uniquely mapped to \([ax + b]\) +\item \(f([ax + b] + [cx + d]) = f([(a + c)x + (b + d)]) = (a + c) + (b + d)\sqrt{2} = (a + b\sqrt{2}) + (c + d\sqrt{2}) = f([ax + b]) + f([cx + d])\) + +\item And via Question Six from section 5.2 above, +\(f([ax + b] \cdot [cx + d]) = f([(ad + bc)x + (2ac + bd)]) = (ad + bc) + (2ac + bd)\sqrt{2} = (a + b\sqrt{2})(c + d\sqrt{2}) = f([ax + b])f([cx + d])\) +\end{itemize} + +\subsection{Question Five} +\label{sec:orgc53207a} +\subsubsection{a} +\label{sec:orgf8f7862} +Since \(\mathds{Q} (\sqrt{3})\) is a subset of \(\mathds{R}\), multiplication and addition are associative, commutative, and distributive. + +The additive identity of \$\mathds{Q} (\sqrt{3}) is \(0 + 0\sqrt{3}\) and the multiplicative identity is \(1 + 0\sqrt{3}\). + +It must be a field since every non-zero element \(r + s \sqrt{3}\) is a unit (by first assuming that the inverse of \(r + s\sqrt{3}\) from the +back of the book, is \(\frac{r}{t} - \frac{s}{t}\sqrt{3}\) with \(t=r^2 - 3s^2\)): + +\begin{align*} +1 &= (r + s\sqrt{3})(\frac{r}{t} - \frac{s}{t}\sqrt{3}) \\ + &= \frac{r^2}{t} - \frac{sr}{t}\sqrt{3} + \frac{sr}{t}\sqrt{3} - \frac{3s^2}{t} \\ + &= \frac{r^2 - 3s^2}{t} \\ + &= 1 +\end{align*} + +\subsubsection{b} +\label{sec:org1d5d4ca} +\begin{enumerate} +\item Quick Lemma +\label{sec:org6e61eec} +In \(\mathds{Q}{x^2 - 3}\), by Corollary 5.5, each congruence class can be rewritten with \(a,b \in \mathds{Q}\): \([ax + b]\). + +\((ax + b)(cx + d) = acx^2 + dax + bcx + bd = acx^2 + (da + bc)x + bd\) + +\begin{equation*} +\polylongdiv[style=A]{acx^2 + (da + bc)x + bd}{x^2 - 3} +\end{equation*} + +Multiplication is thusly defined as \([ax + b] \cdot [cx + d] = [(ad + bc)x + (3ac + bd)]\) + +\item Yeah, it's an isomorphism +\label{sec:org454b3a6} + +Every element in \(\mathds{Q} / (x^2 - 3)\) can be rewritten as a member of the congruence class \([ax + b]\) with \(a, b \in \mathds{Q}\) by Corollary 5.5. + +Then, we can define a function \(f\) such that \(f([rx + s]) = r + s\sqrt{3}\) so that \(f(x) \in \mathds{Q}(\sqrt{3})\). + +\(f\) is thus an isomorphism since (a chance of redemption from my midterm \(\ddot\smile\)): + +\begin{itemize} +\item \(f\) is injective since \(f([ax + b]) = f([cx + d]) \Rightarrow a + b\sqrt{3} = c + d\sqrt{3} \Rightarrow a = c \wedge b = d\) +\item \(f\) is surjective since each \(a + b\sqrt{3}\) is uniquely mapped to \([ax + b]\) +\item \(f([ax + b] + [cx + d]) = f([(a + c)x + (b + d)]) = (a + c) + (b + d)\sqrt{3} = (a + b\sqrt{3}) + (c + d\sqrt{3}) = f([ax + b]) + f([cx + d])\) +\item And from the lemma, \(f([ax + b] \cdot [cx + d]) = f([(ad + bc)x + (3ac + bd)]) = (ad + bc) + (3ac + bd)\sqrt{3} = (a + b\sqrt{3})(c + d\sqrt{3}) = f([ax + b])f([cx + d])\) +\end{itemize} +\end{enumerate} +\end{document}
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Emergency stop. +<read *> + +l.16 \author + {Lizzy Hunt}^^M +*** (cannot \read from terminal in nonstop modes) + + +Here is how much of TeX's memory you used: + 10208 strings out of 477985 + 155314 string characters out of 5839277 + 1849388 words of memory out of 5000000 + 30312 multiletter control sequences out of 15000+600000 + 513462 words of font info for 35 fonts, out of 8000000 for 9000 + 14 hyphenation exceptions out of 8191 + 75i,0n,76p,384b,38s stack positions out of 10000i,1000n,20000p,200000b,200000s +! ==> Fatal error occurred, no output PDF file produced! diff --git a/Homework/math4310/abstract_algebra_midterm_2.org b/Homework/math4310/abstract_algebra_midterm_2.org new file mode 100644 index 0000000..b4ba650 --- /dev/null +++ b/Homework/math4310/abstract_algebra_midterm_2.org @@ -0,0 +1,141 @@ +#+TITLE: Midterm 2 +#+AUTHOR: Lizzy Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} \usepackage{polynom} \usepackage{wasysym} +#+LATEX: \setlength\parindent{0pt} +#+OPTIONS: toc:nil + +* Question One +In $\mathds{Z}_3[x]$, $4x^3 + 4x + 4 \equiv x^3 + x + 1$ +\begin{equation*} +\polylongdiv[style=A]{x^3 + x + 1}{2x^2+1} +\end{equation*} + +$\frac{1}{2}x \equiv_3 2x$ and $\frac{1}{2}x + 1 \equiv_3 (2x + 1)$ + +So, $a(x) = b(x)q(x) + r(x) = (2x^2 + 1)(2x) + (2x + 1)$ + +* Question Two +\begin{equation*} +\polylongdiv[style=A]{x^4 + x^3 + x + 1}{x-2} +\end{equation*} + +Shows that the remainder will be zero when we are in $\mathds{Z}_3[x]$ + +* Question Three +We will use the Euclidean algorithm to find the GCD: +** GCD +\begin{align*} +3x^3 + 2x^2 + 2x + 3 &= (3x - 1)(x^2 + x + 3) + (4x + 1) \\ +(x^2 + x + 3) &\equiv_5 (4x + 1)(4x + 3) + 45 \equiv_5 (4x + 1)(4x + 3) + 0 \\ +\end{align*} + +So, the GCD is (4x + 1) + +** (supplement) Division Algorithm Work +\begin{equation*} +\polylongdiv[style=A]{3x^3 + 2x^2 + 2x + 3}{x^2 + x + 3} +\end{equation*} + +\begin{equation*} +\polylongdiv[style=A]{x^2 + x + 3}{4x + 1} +\end{equation*} + +Check the GCD: + +\begin{equation*} +\polylongdiv[style=A]{3x^3 + 2x^2 + 2x + 3}{4x + 1} +\end{equation*} + +$\frac{3}{4}x^2 + \frac{5}{16}x + \frac{27}{64} \equiv_5 2x^2 + 3$ +and $\frac{165}{64} \equiv_5 0$ + +\begin{equation*} +\polylongdiv[style=A]{x^2 + x + 3}{4x + 1} +\end{equation*} + +$\frac{1}{4}x + \frac{3}{16} \equiv_5 4x + 3$ +and $\frac{45}{16} \equiv_5 0$. + +* Question Four +** a +$\mathds{Z}_3[x]$ is a field by Theorem 2.8. + +There are no roots of $2x^3 + x + 1$ in $\mathds{Z}_3$, so by Theorem 5.10 $\mathds{Z}_3[x] / (2x^3 + x + 1)$ is a field, as it is +irreducible by Corollary 4.19. + +** b +Since we've proven $\mathds{Z}_3[x] / (2x^3 + x + 1)$ is a field, we know that $[2x + 1]$ must be a unit. + +By similar reasoning to the proof of Theorem 5.10 (1), $gcd(2x + 1, 2x^3 + x + 1) = 1$ + +Then, + +\begin{equation*} +\polylongdiv[style=A]{2x^3 + x + 1}{2x + 1} +\end{equation*} + +Shows that: +\begin{align*} +2x^3 + x + 1 &= (2x + 1)(x^2 + x) + 1 \\ +1 &= (2x^3 + x + 1) + (2x+1)(-x^2 - x) \\ +1 - (2x^3 + x + 1) &= (2x + 1)(-x^2 - x) \\ +1 &\equiv_{2x^3 + x + 1} (2x+1)(-x^2 - x) +\end{align*} +and thus, by similar logic again found in the proof mentioned before, $[-x^2 - x] = [2x^2 + 2x]$ must be the inverse. + +As a sanity check, + +\begin{equation*} +\polylongdiv[style=A]{2x^3 + x + 1}{2x^2 + 2x} +\end{equation*} + +shows that the remainder is a unit in $\mathds{Z}[3]$. + +* Question Five +Firstly, $\mathds{Z}_5[x]$ is a field by Theorem 2.8. + +** a +There are no roots of $x^2 + 2x + 3$ in $\mathds{Z}_5$, so by Theorem 5.10 it is irreducible. + +$f_1 : (0, 1, 2, 3, 4) \rightarrow (3, 1, 1, 3, 2)$ + +** b +This is reducible since $1$ is a root. + +\begin{equation*} +\polylongdiv[style=A]{x^3 + x + 3}{x - 1} +\end{equation*} + +Thus, $f_2(x) = (x + 4)(x^2 + x + 2)$ + + +* Question Six +Following pages 137 - 138 of the book... + +By Corollary 4.19 we know $(x^2 + 1)$ is irreducible in $\mathds{R}[x]$ since its only roots are in $\mathds{C}$: $\pm i$. + +Because of Corollary 5.12, we know that there is an extension field $K$ that contains a root to $(x^2 + 1)$. Namely, +some $\alpha = [x]$. By Corollary 5.5, each element can be rewritten as $[ax + b]$ with $a, b \in \mathds{R}$. +We can create a mapping $f$ such that $[a + bx] \rightarrow [a] + [b][x] = a + b \alpha$ is unique and $f^{-1}(a + b \alpha) \rightarrow [a + bx]$ (bijection). + +Additionally, we can show that $f([a + bx]) + f([c + dx]) = (a + b \alpha) + (c + d \alpha) = (a + c) + (b + d) \alpha = f([(a + c)x + (b + d)])$. + +\begin{equation*} +[ax + b][cx + b] = [acx^2 + abx + bcx + bd] +\end{equation*} + +\begin{equation*} +\polylongdiv[style=A]{acx^2 + abx + bcx + bd}{x^2 + 1} +\end{equation*} + +So, multiplication in $K$ is given: + +\begin{equation*} +[ax + b][cx + b] = [(ab + bc)x + ac - bd] +\end{equation*} + +Then, we can show that by definition of $\alpha$, $f([a + bx]) \cdot f([c + dx]) = (a + b \alpha) \cdot (c + d \alpha) = (ac + ad \alpha + bc \alpha + bd \alpha^2) = (ac - bd + (ad + bc)\alpha) = f([(ab + bc)x + ac - bd]) = f([a + bx][c + dx])$. + +Now, replacing our work with $\alpha = i$, $f$ is an isomorphism from $\mathds{R}/(x^2 + 1)$ to $\mathds{C}$ since it is a bijection and satisfies the addition and multiplication rules. + diff --git a/Homework/math4310/abstract_algebra_midterm_2.pdf b/Homework/math4310/abstract_algebra_midterm_2.pdf Binary files differnew file mode 100644 index 0000000..a2f8126 --- /dev/null +++ b/Homework/math4310/abstract_algebra_midterm_2.pdf diff --git a/Homework/math4310/abstract_algebra_midterm_2.tex b/Homework/math4310/abstract_algebra_midterm_2.tex new file mode 100644 index 0000000..a3f0a2f --- /dev/null +++ b/Homework/math4310/abstract_algebra_midterm_2.tex @@ -0,0 +1,176 @@ +% Created 2023-10-07 Sat 14:55 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} \usepackage{polynom} \usepackage{wasysym} +\author{Lizzy Hunt} +\date{\today} +\title{Midterm 2} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Midterm 2}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.7-pre)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Question One} +\label{sec:orgd83a31d} +In \(\mathds{Z}_3[x]\), \(4x^3 + 4x + 4 \equiv x^3 + x + 1\) +\begin{equation*} +\polylongdiv[style=A]{x^3 + x + 1}{2x^2+1} +\end{equation*} + +\(\frac{1}{2}x \equiv_3 2x\) and \(\frac{1}{2}x + 1 \equiv_3 (2x + 1)\) + +So, \(a(x) = b(x)q(x) + r(x) = (2x^2 + 1)(2x) + (2x + 1)\) + +\section{Question Two} +\label{sec:org245f338} +\begin{equation*} +\polylongdiv[style=A]{x^4 + x^3 + x + 1}{x-2} +\end{equation*} + +Shows that the remainder will be zero when we are in \(\mathds{Z}_3[x]\) + +\section{Question Three} +\label{sec:org154bff9} +We will use the Euclidean algorithm to find the GCD: +\subsection{GCD} +\label{sec:orga7765bb} +\begin{align*} +3x^3 + 2x^2 + 2x + 3 &= (3x - 1)(x^2 + x + 3) + (4x + 1) \\ +(x^2 + x + 3) &\equiv_5 (4x + 1)(4x + 3) + 45 \equiv_5 (4x + 1)(4x + 3) + 0 \\ +\end{align*} + +So, the GCD is (4x + 1) + +\subsection{(supplement) Division Algorithm Work} +\label{sec:orgdafc72b} +\begin{equation*} +\polylongdiv[style=A]{3x^3 + 2x^2 + 2x + 3}{x^2 + x + 3} +\end{equation*} + +\begin{equation*} +\polylongdiv[style=A]{x^2 + x + 3}{4x + 1} +\end{equation*} + +Check the GCD: + +\begin{equation*} +\polylongdiv[style=A]{3x^3 + 2x^2 + 2x + 3}{4x + 1} +\end{equation*} + +\(\frac{3}{4}x^2 + \frac{5}{16}x + \frac{27}{64} \equiv_5 2x^2 + 3\) +and \(\frac{165}{64} \equiv_5 0\) + +\begin{equation*} +\polylongdiv[style=A]{x^2 + x + 3}{4x + 1} +\end{equation*} + +\(\frac{1}{4}x + \frac{3}{16} \equiv_5 4x + 3\) +and \(\frac{45}{16} \equiv_5 0\). + +\section{Question Four} +\label{sec:org9492a2d} +\subsection{a} +\label{sec:orgc2e7831} +\(\mathds{Z}_3[x]\) is a field by Theorem 2.8. + +There are no roots of \(2x^3 + x + 1\) in \(\mathds{Z}_3\), so by Theorem 5.10 \(\mathds{Z}_3[x] / (2x^3 + x + 1)\) is a field, as it is +irreducible by Corollary 4.19. + +\subsection{b} +\label{sec:org68f838e} +Since we've proven \(\mathds{Z}_3[x] / (2x^3 + x + 1)\) is a field, we know that \([2x + 1]\) must be a unit. + +By similar reasoning to the proof of Theorem 5.10 (1), \(gcd(2x + 1, 2x^3 + x + 1) = 1\) + +Then, + +\begin{equation*} +\polylongdiv[style=A]{2x^3 + x + 1}{2x + 1} +\end{equation*} + +Shows that: +\begin{align*} +2x^3 + x + 1 &= (2x + 1)(x^2 + x) + 1 \\ +1 &= (2x^3 + x + 1) + (2x+1)(-x^2 - x) \\ +1 - (2x^3 + x + 1) &= (2x + 1)(-x^2 - x) \\ +1 &\equiv_{2x^3 + x + 1} (2x+1)(-x^2 - x) +\end{align*} +and thus, by similar logic again found in the proof mentioned before, \([-x^2 - x] = [2x^2 + 2x]\) must be the inverse. + +As a sanity check, + +\begin{equation*} +\polylongdiv[style=A]{2x^3 + x + 1}{2x^2 + 2x} +\end{equation*} + +shows that the remainder is a unit in \(\mathds{Z}[3]\). + +\section{Question Five} +\label{sec:orgaf8ce04} +Firstly, \(\mathds{Z}_5[x]\) is a field by Theorem 2.8. + +\subsection{a} +\label{sec:orgf579bc7} +There are no roots of \(x^2 + 2x + 3\) in \(\mathds{Z}_5\), so by Theorem 5.10 it is irreducible. + +\(f_1 : (0, 1, 2, 3, 4) \rightarrow (3, 1, 1, 3, 2)\) + +\subsection{b} +\label{sec:orgb0b2569} +This is reducible since \(1\) is a root. + +\begin{equation*} +\polylongdiv[style=A]{x^3 + x + 3}{x - 1} +\end{equation*} + +Thus, \(f_2(x) = (x + 4)(x^2 + x + 2)\) + + +\section{Question Six} +\label{sec:org009bcbb} +Following pages 137 - 138 of the book\ldots{} + +By Corollary 4.19 we know \((x^2 + 1)\) is irreducible in \(\mathds{R}[x]\) since its only roots are in \(\mathds{C}\): \(\pm i\). + +Because of Corollary 5.12, we know that there is an extension field \(K\) that contains a root to \((x^2 + 1)\). Namely, +some \(\alpha = [x]\). By Corollary 5.5, each element can be rewritten as \([ax + b]\) with \(a, b \in \mathds{R}\). +We can create a mapping \(f\) such that \([a + bx] \rightarrow [a] + [b][x] = a + b \alpha\) is unique and \(f^{-1}(a + b \alpha) \rightarrow [a + bx]\) (bijection). + +Additionally, we can show that \(f([a + bx]) + f([c + dx]) = (a + b \alpha) + (c + d \alpha) = (a + c) + (b + d) \alpha = f([(a + c)x + (b + d)])\). + +\begin{equation*} +[ax + b][cx + b] = [acx^2 + abx + bcx + bd] +\end{equation*} + +\begin{equation*} +\polylongdiv[style=A]{acx^2 + abx + bcx + bd}{x^2 + 1} +\end{equation*} + +So, multiplication in \(K\) is given: + +\begin{equation*} +[ax + b][cx + b] = [(ab + bc)x + ac - bd] +\end{equation*} + +Then, we can show that by definition of \(\alpha\), \(f([a + bx]) \cdot f([c + dx]) = (a + b \alpha) \cdot (c + d \alpha) = (ac + ad \alpha + bc \alpha + bd \alpha^2) = (ac - bd + (ad + bc)\alpha) = f([(ab + bc)x + ac - bd]) = f([a + bx][c + dx])\). + +Now, replacing our work with \(\alpha = i\), \(f\) is an isomorphism from \(\mathds{R}/(x^2 + 1)\) to \(\mathds{C}\) since it is a bijection and satisfies the addition and multiplication rules. +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/alg_structures_assn_2.org b/Homework/math4310/alg_structures_assn_2.org new file mode 100644 index 0000000..d7dee4c --- /dev/null +++ b/Homework/math4310/alg_structures_assn_2.org @@ -0,0 +1,135 @@ +#+TITLE: Assignment Two +#+AUTHOR: Logan Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} +#+LATEX: \setlength\parindent{0pt} + + +* Section 1.3 +** Question 3 +701, 1009, 1949, 1951 are all prime +** Question 7 +\begin{align*} +p | a \Rightarrow np &= a \\ +p | a + bc \Rightarrow mp &= a + bc \\ +mp &= np + bc \\ +mp - np &= bc \\ +p(m - n) &= bc +\end{align*} + +Since $bc$ is a multiple of $p$, and $p$ is prime, by Theorem 1.5, $p | b$ or $p | c$. +** Question 15 +If $p | a^n \Rightarrow p | a \cdot a \dotsc a$ then by corollary 1.6, $p | a$. Then, $a = pm$ and +$a^n = p^n \cdot m^n$. $p^n$ is a factor of $a^n$ and thus $p^n | a^n$. + +** Question 17 + +From the Fundamental Theorem of Arithmetic, both $a$ and $b$ must be a product of primes such that +$a = (p \cdot p_1 \cdot p_2 \dotsc p_i)$ and $b = (p \cdot q_1 \cdot q_2 \dotsc q_j)$ with each $p_i$ and $q_j$ being prime. + +Then, $a^2 = (p \cdot p_1 \cdot p_2 \dotsc p_r) \cdot (p \cdot p_1 \cdot p_2 \dots p_r)$ and $b^2 = (p \cdot q_1 \cdot q_2 \dotsc q_j) \cdot (p \cdot q_1 \cdot q_2 \dotsc q_j)$. +$p^2$ is then a common factor of $a^2$ and $b^2$, and since each other factor ($p_i^2$, $q_i^2$) is a square of a prime, there +can be no other greater common divisor than $p^2$. + +Therefore, $(a, b) = p \Rightarrow (a^2, b^2) = p^2$ when p is prime. + +** Question 30 +*** a +Firstly assume that there are $a,b \ni a^2 = 2b^2$. Then, $a^2 = p_1 p_2 \dotsc p_r$ and $2b^2 = q_1 q_2 \dotsc q_s$, +and by the Fundamental Theorem of Arithmetic, every $p_i = \pm q_j$. Since $a^2$ is even as it is equal +to $2b^2$, let $p_1$ be the factor corresponding to a power of $2$. Then $p_1 = 2^n$ and $n$ must be a +multiple of $2$ since $a^2 = 2^n \dotsc \Rightarrow a = 2^{\frac{n}{2}} \dotsc$ + +However, $2b^2 = \pm 2^n \dotsc$ implies that $b^2 = \pm 2^{n-1} \dotsc$ and from similar reasoning $n-1$ must also +be a multiple of $2$. + +This is a contradiction - not both $n$ and $n-1$ can be multiples of $2$! + +*** b +Just reformat it: + +\begin{equation*} +\sqrt{2} = \frac{a}{b} \Rightarrow 2 = \frac{a^2}{b^2} \Rightarrow 2b^2 = a^2 +\end{equation*} + + +* Section 2.1 +** Question 2 +*** a +\begin{equation*} +6k + 5 \equiv_4 6 + 5 \equiv_4 11 \equiv_4 3 +\end{equation*} + +*** b +\begin{equation*} +2r + 3s \equiv_{10} 2(3) + 3(-7) \equiv_{10} 6 - 21 \equiv_{10} -15 \equiv_{10} 5 +\end{equation*} + +** Question 3b +\begin{align*} +& 10(0) + 9(0) + 8(3) + 7(1) + 6(1) + 5(0) + 4(5) + 3(5) + 2(9) + 5 \\ +&\equiv_{11 }24 + 7 + 6 + 20 + 15 + 18 + 5 \\ +&\equiv_{11} 95 \\ +&\equiv_{11} 7 +\end{align*} + +Invalid ISBN + +** Question 5 +*** a +Theorem 2.2 states that if $a \equiv_4 b$, and $c \equiv_4 d$, then $ac \equiv_4 bd$. + +Since $5 \equiv_4 1$ and $5 \cdot 5 \equiv_4 1 \cdot 1$, then $5 \cdot 5 \cdot 5 \equiv_4 1 \cdot 1 \cdot 1$. + +We can continue chaining these together until we find $5^{2000} \equiv_4 1^{2000}$, and thus [5^{2000}] = [1] in $\mathds{Z}_4$. +*** b +By repeating the same process as in a, $4 \equiv_5 4$ and $4^2 \equiv_5 1$. Then, $4^3 \equiv_5 4 \cdot 1$. Then, $4^4 \equiv_5 4^2 \Rightarrow 4^4 \equiv_5 1$. + +In general as we keep chaining on and because of Theorem 2.2, even powers of 4 will be equivalent mod 5 to 1, +and odd powers of 4 will be equivalent mod 5 to 4. + +Therefore, $4^{2001} \equiv_5 1$ and $[4^{2001}] = [1]$ in $\mathds{Z}_5$. +** Question 7 +If $a \in \mathds{Z}$ then $a \equiv_4 m$ with $m \in {1,2,3,4}$. Then, by Theorem 2.2 again, $a^2 \equiv_4 m^2$. + +$[m^2] \in \mathds{Z}_4$ must be equivalent to any ${[1^2], [2^2], [3^2], [4^2]} = {[1], [0], [1], [0]}$. + +Therefore, $[a^2]$ cannot be in ${[3], [4]} \subset {[2], [3], [4]}$ + +** Question 14 +*** a +A simple python script will prove this is false: + +\begin{verbatim} +seen = set() +for n in range(1, 10): + for a in range(0, 10): + for b in range(0, 10): + seenfoo = (a, b, n) in seen or (b, a, n) in seen + if (a * b) % n == 0 and a % n != 0 and b % n != 0 and not seenfoo: + seen.add((a, b, n)) + print(f"a={a}, b={b}, n={n}") +\end{verbatim} + +And we receive several counterexamples: + +\begin{verbatim} +a=2, b=2, n=4 +a=2, b=6, n=4 +a=6, b=6, n=4 +a=2, b=3, n=6 +a=2, b=9, n=6 +... +a=2, b=4, n=8 +a=4, b=6, n=8 +a=3, b=3, n=9 +a=3, b=6, n=9 +a=6, b=6, n=9 +\end{verbatim} + +*** b +If $ab \equiv_n 0$, then $ab = mn + 0$ for some $m \in \mathds{Z}$ by definition. + +Then, $ab = mn$ implies that $ab$ is a multiple of $n$, and since $n$ is prime, then by Theorem 1.8, $n | ab$ implies that $n | a$ or $n | b$. + + diff --git a/Homework/math4310/alg_structures_assn_2.pdf b/Homework/math4310/alg_structures_assn_2.pdf Binary files differnew file mode 100644 index 0000000..cd405a0 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_2.pdf diff --git a/Homework/math4310/alg_structures_assn_2.tex b/Homework/math4310/alg_structures_assn_2.tex new file mode 100644 index 0000000..fa7ea3e --- /dev/null +++ b/Homework/math4310/alg_structures_assn_2.tex @@ -0,0 +1,180 @@ +% Created 2023-01-25 Wed 08:50 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notga \usepackage{ dsfont } \usepackage{amsmath} +\author{Logan Hunt} +\date{\today} +\title{Assignment Two} +\hypersetup{ + pdfauthor={Logan Hunt}, + pdftitle={Assignment Two}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.5.5)}, + pdflang={English}} +\begin{document} + +\maketitle +\tableofcontents + +\setlength\parindent{0pt} + + +\section{Section 1.3} +\label{sec:orgb642b1a} +\subsection{Question 3} +\label{sec:orgefa83b9} +701, 1009, 1949, 1951 are all prime +\subsection{Question 7} +\label{sec:org19f664b} +\begin{align*} +p | a \Rightarrow np &= a \\ +p | a + bc \Rightarrow mp &= a + bc \\ +mp &= np + bc \\ +mp - np &= bc \\ +p(m - n) &= bc +\end{align*} + +Since \(bc\) is a multiple of \(p\), and \(p\) is prime, by Theorem 1.5, \(p | b\) or \(p | c\). +\subsection{Question 15} +\label{sec:orgec25485} +If \(p | a^n \Rightarrow p | a \cdot a \dotsc a\) then by corollary 1.6, \(p | a\). Then, \(a = pm\) and +\(a^n = p^n \cdot m^n\). \(p^n\) is a factor of \(a^n\) and thus \(p^n | a^n\). + +\subsection{Question 17} +\label{sec:orgf0ee3ce} + +From the Fundamental Theorem of Arithmetic, both \(a\) and \(b\) must be a product of primes such that +\(a = (p \cdot p_1 \cdot p_2 \dotsc p_i)\) and \(b = (p \cdot q_1 \cdot q_2 \dotsc q_j)\) with each \(p_i\) and \(q_j\) being prime. + +Then, \(a^2 = (p \cdot p_1 \cdot p_2 \dotsc p_r) \cdot (p \cdot p_1 \cdot p_2 \dotsc p_r)\) and \(b^2 = (p \cdot q_1 \cdot q_2 \dotsc q_j) \cdot (p \cdot q_1 \cdot q_2 \dotsc q_j)\). +\(p^2\) is then a common factor of \(a^2\) and \(b^2\), and since each other factor (\(p_i^2\), \(q_i^2\)) is a square of a prime, there +can be no other greater common divisor than \(p^2\). + +Therefore, \((a, b) = p \Rightarrow (a^2, b^2) = p^2\) when p is prime. + +\subsection{Question 30} +\label{sec:org711c1fd} +\subsubsection{a} +\label{sec:org622b53c} +Firstly assume that there are \(a,b \ni a^2 = 2b^2\). Then, \(a^2 = p_1 p_2 \dotsc p_r\) and \(2b^2 = q_1 q_2 \dotsc q_s\), +and by the Fundamental Theorem of Arithmetic, every \(p_i = \pm q_j\). Since \(a^2\) is even as it is equal +to \(2b^2\), let \(p_1\) be the factor corresponding to a power of \(2\). Then \(p_1 = 2^n\) and \(n\) must be a +multiple of \(2\) since \(a^2 = 2^n \dotsc \Rightarrow a = 2^{\frac{n}{2}} \dotsc\) + +However, \(2b^2 = \pm 2^n \dotsc\) implies that \(b^2 = \pm 2^{n-1} \dotsc\) and from similar reasoning \(n-1\) must also +be a multiple of \(2\). + +This is a contradiction - not both \(n\) and \(n-1\) can be multiples of \(2\)! + +\subsubsection{b} +\label{sec:orgfba7c43} +Just reformat it: + +\begin{equation*} +\sqrt{2} = \frac{a}{b} \Rightarrow 2 = \frac{a^2}{b^2} \Rightarrow 2b^2 = a^2 +\end{equation*} + + +\section{Section 2.1} +\label{sec:orgd42fe0f} +\subsection{Question 2} +\label{sec:org8c3b581} +\subsubsection{a} +\label{sec:orgc7b35b9} +\begin{equation*} +6k + 5 \equiv_4 6 + 5 \equiv_4 11 \equiv_4 3 +\end{equation*} + +\subsubsection{b} +\label{sec:org07ec8aa} +\begin{equation*} +2r + 3s \equiv_{10} 2(3) + 3(-7) \equiv_{10} 6 - 21 \equiv_{10} -15 \equiv_{10} 5 +\end{equation*} + +\subsection{Question 3b} +\label{sec:org29b1c99} +\begin{align*} +& 10(0) + 9(0) + 8(3) + 7(1) + 6(1) + 5(0) + 4(5) + 3(5) + 2(9) + 5 \\ +&\equiv_{11 }24 + 7 + 6 + 20 + 15 + 18 + 5 \\ +&\equiv_{11} 95 \\ +&\equiv_{11} 7 +\end{align*} + +Invalid ISBN + +\subsection{Question 5} +\label{sec:org37d83f3} +\subsubsection{a} +\label{sec:org770db68} +Theorem 2.2 states that if \(a \equiv_4 b\), and \(c \equiv_4 d\), then \(ac \equiv_4 bd\). + +Since \(5 \equiv_4 1\) and \(5 \cdot 5 \equiv_4 1 \cdot 1\), then \(5 \cdot 5 \cdot 5 \equiv_4 1 \cdot 1 \cdot 1\). + +We can continue chaining these together until we find \(5^{2000} \equiv_4 1^{2000}\), and thus [5\textsuperscript{2000}] = [1] in \(\mathds{Z}_4\). +\subsubsection{b} +\label{sec:org12acb79} +By repeating the same process as in a, \(4 \equiv_5 4\) and \(4^2 \equiv_5 1\). Then, \(4^3 \equiv_5 4 \cdot 1\). Then, \(4^4 \equiv_5 4^2 \Rightarrow 4^4 \equiv_5 1\). + +In general as we keep chaining on and because of Theorem 2.2, even powers of 4 will be equivalent mod 5 to 1, +and odd powers of 4 will be equivalent mod 5 to 4. + +Therefore, \(4^{2001} \equiv_5 1\) and \([4^{2001}] = [1]\) in \(\mathds{Z}_5\). +\subsection{Question 7} +\label{sec:orgc6a9940} +If \(a \in \mathds{Z}\) then \(a \equiv_4 m\) with \(m \in {1,2,3,4}\). Then, by Theorem 2.2 again, \(a^2 \equiv_4 m^2\). + +\([m^2] \in \mathds{Z}_4\) must be equivalent to any \({[1^2], [2^2], [3^2], [4^2]} = {[1], [0], [1], [0]}\). + +Therefore, \([a^2]\) cannot be in \({[3], [4]} \subset {[2], [3], [4]}\) + +\subsection{Question 14} +\label{sec:org0f658a6} +\subsubsection{a} +\label{sec:org9ee67bf} +A simple python script will prove this is false: + +\begin{verbatim} +seen = set() +for n in range(1, 10): + for a in range(0, 10): + for b in range(0, 10): + seenfoo = (a, b, n) in seen or (b, a, n) in seen + if (a * b) % n == 0 and a % n != 0 and b % n != 0 and not seenfoo: + seen.add((a, b, n)) + print(f"a={a}, b={b}, n={n}") +\end{verbatim} + +And we receive several counterexamples: + +\begin{verbatim} +a=2, b=2, n=4 +a=2, b=6, n=4 +a=6, b=6, n=4 +a=2, b=3, n=6 +a=2, b=9, n=6 +... +a=2, b=4, n=8 +a=4, b=6, n=8 +a=3, b=3, n=9 +a=3, b=6, n=9 +a=6, b=6, n=9 +\end{verbatim} + +\subsubsection{b} +\label{sec:org767f9d7} +If \(ab \equiv_n 0\), then \(ab = mn + 0\) for some \(m \in \mathds{Z}\) by definition. + +Then, \(ab = mn\) implies that \(ab\) is a multiple of \(n\), and since \(n\) is prime, then by Theorem 1.8, \(n | ab\) implies that \(n | a\) or \(n | b\). +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/alg_structures_assn_3.org b/Homework/math4310/alg_structures_assn_3.org new file mode 100644 index 0000000..c0165a0 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_3.org @@ -0,0 +1,115 @@ +#+TITLE: Assignment Three +#+AUTHOR: Logan Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} +#+LATEX: \setlength\parindent{0pt} +#+OPTIONS: toc:nil + +* Section 2.2 +** Question One +*** b +| \oplus | 0 | 1 | 2 | 3 | +| 0 | 0 | 1 | 2 | 3 | +| 1 | 1 | 2 | 3 | 0 | +| 2 | 2 | 3 | 0 | 1 | +| 3 | 3 | 0 | 1 | 2 | + +| \odot | 0 | 1 | 2 | 3 | +| 0 | 0 | 0 | 0 | 0 | +| 1 | 0 | 1 | 2 | 3 | +| 2 | 0 | 2 | 0 | 2 | +| 3 | 0 | 3 | 2 | 1 | + +*** c +| \oplus | 0 | 1 | 2 | 3 | 4 | 5 | 6 | +| 0 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | +| 1 | 1 | 2 | 3 | 4 | 5 | 6 | 0 | +| 2 | 2 | 3 | 4 | 5 | 6 | 0 | 1 | +| 3 | 3 | 4 | 5 | 6 | 0 | 1 | 2 | +| 4 | 4 | 5 | 6 | 0 | 1 | 2 | 3 | +| 5 | 5 | 6 | 0 | 1 | 2 | 3 | 4 | +| 6 | 6 | 0 | 1 | 2 | 3 | 4 | 5 | + +| \odot | 0 | 1 | 2 | 3 | 4 | 5 | 6 | +| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | +| 1 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | +| 2 | 0 | 2 | 4 | 6 | 1 | 3 | 5 | +| 3 | 0 | 3 | 6 | 2 | 5 | 1 | 4 | +| 4 | 0 | 4 | 1 | 5 | 2 | 6 | 3 | +| 5 | 0 | 5 | 3 | 1 | 6 | 4 | 2 | +| 6 | 0 | 6 | 5 | 4 | 3 | 2 | 1 | + +** Question Three +$x = [1], [3], [5], [7]$ + +** Question Five +$x = [1], [2], [4], [5]$ + +** Question Eight +$x = [1], [2], [6], [7]$ + +** Question Eleven +*** b +$x = [0], [1], [2], [3]$ +** Question Fifteen +*** c +From the Binomial Theorem, + +\begin{align*} +(a + b)^5 &= a^5 + 5a^4 b + 10a^3 b^2 + 10a^2 b^3 + 5ab^4 + b^5 +\end{align*} + +Then, +\begin{equation*} +(a + b)^5 &\equiv_5 (a^5 + 5a^4 b + 10a^3 b^2 + 10a^2 b^3 + 5ab^4 + b^5) \\ +&\equiv_5 (a^5 + b^5) \\ +\end{equation*} + +since each of the terms $5a^4 b, 10a^3 b^2, 10a^2 b^3, 5ab^4$ are zero as $5 \equiv_5 0$ and $10 \equiv_5 0$. + + + +* Section 2.3 +** Question One +*** b +$[1], [3], [5], [7]$ since $[7 * 7] = [49] = [1]$, $[5 * 5] = [25] = [1]$, $[3 * 3] = [9] = [1]$, and +$[1 * 1] = [1]$. +** Question Two +*** b +$[2], [4], [6]$ since $[2 * 4] = [8] = [0]$, $[4 * 4] = [16] = [0]$, and $[6 * 4] = [24] = [0]$. +** Question Eight +*** a +1. $2x = 1$ +2. $2x = 3$ +3. $2x = 5$ +*** b +Yes, each one is equivalent to 0 when $x = 6$. +** Question Nine +*** a +By definition, there exists $b$, the inverse of $a$, such that $ab = 1$. +Assume that $a$ is a zero divisor, then there exists $c \neq 0$ +such that $ac = 0$. Then, $(ab)c = 0b \Rightarrow (1)(c) = 0$ implies that $c = 0$, which is a contradiction. +*** b +By definition, there exists $b$, with $b \neq 0$ such that $ab = 0$. +Assume that $a$ is a unit, then there exists $c$ such that $ac = 1$. +Then, $(b)ac = 1b \Rightarrow 0c = b$ implies that $b = 0$, which is a contradiction. + +** Question Eleven +By definition of $a$ being a unit, there exists $ay = 1$ with $y$ being an inverse of $a$. +By multiplying our target $(y)ax = (y)b \Rightarrow x = yb$. + +To prove this is unique, assume that $k$ and $l$ are solutions of $ax = b$. Then, $ak = b$ and $al = b$. Since $a$ is a unit, by using our +previous strategy, $(y)ak = (y)b$ and $(y)al = (y)b$, so $k = yb$ and $l = yb$ and thus $k = l$. + + +* Chapter 13 +** A2 +As $p | c \Rightarrow c = pk$, and $p | c \Rightarrow c = ql$ then $pk = ql$ and thus by Theorem 1.5 since $p$ and $q$ are prime $p | l$ +or $p | q$ and $q | p$ or $q | k$, but since $p$ and $q$ are prime, then it must be that only $p | l$ and $q | k$. + +Since $p | l$ then $l = mp$ and $c = ql \Rightarrow c = qmp$ and $qp$ is a factor of $c$. + +** A3 (a) +GO = 0715 + +715^3 (mod 2773) = 107 diff --git a/Homework/math4310/alg_structures_assn_3.pdf b/Homework/math4310/alg_structures_assn_3.pdf Binary files differnew file mode 100644 index 0000000..99e66c1 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_3.pdf diff --git a/Homework/math4310/alg_structures_assn_3.tex b/Homework/math4310/alg_structures_assn_3.tex new file mode 100644 index 0000000..bb9c222 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_3.tex @@ -0,0 +1,183 @@ +% Created 2023-01-31 Tue 22:49 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} +\author{Logan Hunt} +\date{\today} +\title{Assignment Three} +\hypersetup{ + pdfauthor={Logan Hunt}, + pdftitle={Assignment Three}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Section 2.2} +\label{sec:orgfecc6e5} +\subsection{Question One} +\label{sec:orgd22e42b} +\subsubsection{b} +\label{sec:org757c583} +\begin{center} +\begin{tabular}{rrrrr} +\(\oplus\) & 0 & 1 & 2 & 3\\[0pt] +0 & 0 & 1 & 2 & 3\\[0pt] +1 & 1 & 2 & 3 & 0\\[0pt] +2 & 2 & 3 & 0 & 1\\[0pt] +3 & 3 & 0 & 1 & 2\\[0pt] +\end{tabular} +\end{center} + +\begin{center} +\begin{tabular}{rrrrr} +\(\odot\) & 0 & 1 & 2 & 3\\[0pt] +0 & 0 & 0 & 0 & 0\\[0pt] +1 & 0 & 1 & 2 & 3\\[0pt] +2 & 0 & 2 & 0 & 2\\[0pt] +3 & 0 & 3 & 2 & 1\\[0pt] +\end{tabular} +\end{center} + +\subsubsection{c} +\label{sec:org603554a} +\begin{center} +\begin{tabular}{rrrrrrrr} +\(\oplus\) & 0 & 1 & 2 & 3 & 4 & 5 & 6\\[0pt] +0 & 0 & 1 & 2 & 3 & 4 & 5 & 6\\[0pt] +1 & 1 & 2 & 3 & 4 & 5 & 6 & 0\\[0pt] +2 & 2 & 3 & 4 & 5 & 6 & 0 & 1\\[0pt] +3 & 3 & 4 & 5 & 6 & 0 & 1 & 2\\[0pt] +4 & 4 & 5 & 6 & 0 & 1 & 2 & 3\\[0pt] +5 & 5 & 6 & 0 & 1 & 2 & 3 & 4\\[0pt] +6 & 6 & 0 & 1 & 2 & 3 & 4 & 5\\[0pt] +\end{tabular} +\end{center} + +\begin{center} +\begin{tabular}{rrrrrrrr} +\(\odot\) & 0 & 1 & 2 & 3 & 4 & 5 & 6\\[0pt] +0 & 0 & 0 & 0 & 0 & 0 & 0 & 0\\[0pt] +1 & 0 & 1 & 2 & 3 & 4 & 5 & 6\\[0pt] +2 & 0 & 2 & 4 & 6 & 1 & 3 & 5\\[0pt] +3 & 0 & 3 & 6 & 2 & 5 & 1 & 4\\[0pt] +4 & 0 & 4 & 1 & 5 & 2 & 6 & 3\\[0pt] +5 & 0 & 5 & 3 & 1 & 6 & 4 & 2\\[0pt] +6 & 0 & 6 & 5 & 4 & 3 & 2 & 1\\[0pt] +\end{tabular} +\end{center} + +\subsection{Question Three} +\label{sec:org6ac99a4} +\(x = [1], [3], [5], [7]\) + +\subsection{Question Five} +\label{sec:org69e894a} +\(x = [1], [2], [4], [5]\) + +\subsection{Question Eight} +\label{sec:org26350fa} +\(x = [1], [2], [6], [7]\) + +\subsection{Question Eleven} +\label{sec:orgcd603cc} +\subsubsection{b} +\label{sec:org2896606} +\(x = [0], [1], [2], [3]\) +\subsection{Question Fifteen} +\label{sec:org5bca8ba} +\subsubsection{c} +\label{sec:org830aeb3} +From the Binomial Theorem, + +\begin{align*} +(a + b)^5 &= a^5 + 5a^4 b + 10a^3 b^2 + 10a^2 b^3 + 5ab^4 + b^5 +\end{align*} + +Then, +\begin{equation*} +(a + b)^5 &\equiv_5 (a^5 + 5a^4 b + 10a^3 b^2 + 10a^2 b^3 + 5ab^4 + b^5) \\ +&\equiv_5 (a^5 + b^5) \\ +\end{equation*} + +since each of the terms \(5a^4 b, 10a^3 b^2, 10a^2 b^3, 5ab^4\) are zero as \(5 \equiv_5 0\) and \(10 \equiv_5 0\). + + + +\section{Section 2.3} +\label{sec:org7ebf66c} +\subsection{Question One} +\label{sec:orge906711} +\subsubsection{b} +\label{sec:orgddb4d23} +\([1], [3], [5], [7]\) since \([7 * 7] = [49] = [1]\), \([5 * 5] = [25] = [1]\), \([3 * 3] = [9] = [1]\), and +\([1 * 1] = [1]\). +\subsection{Question Two} +\label{sec:org4efa77f} +\subsubsection{b} +\label{sec:org41d490d} +\([2], [4], [6]\) since \([2 * 4] = [8] = [0]\), \([4 * 4] = [16] = [0]\), and \([6 * 4] = [24] = [0]\). +\subsection{Question Eight} +\label{sec:org27e3ed4} +\subsubsection{a} +\label{sec:orgeac97d5} +\begin{enumerate} +\item \(2x = 1\) +\item \(2x = 3\) +\item \(2x = 5\) +\end{enumerate} +\subsubsection{b} +\label{sec:orgb99f90c} +Yes, each one is equivalent to 0 when \(x = 6\). +\subsection{Question Nine} +\label{sec:orge8d0de5} +\subsubsection{a} +\label{sec:org8045c18} +By definition, there exists \(b\), the inverse of \(a\), such that \(ab = 1\). +Assume that \(a\) is a zero divisor, then there exists \(c \neq 0\) +such that \(ac = 0\). Then, \((ab)c = 0b \Rightarrow (1)(c) = 0\) implies that \(c = 0\), which is a contradiction. +\subsubsection{b} +\label{sec:orgc5282b2} +By definition, there exists \(b\), with \(b \neq 0\) such that \(ab = 0\). +Assume that \(a\) is a unit, then there exists \(c\) such that \(ac = 1\). +Then, \((b)ac = 1b \Rightarrow 0c = b\) implies that \(b = 0\), which is a contradiction. + +\subsection{Question Eleven} +\label{sec:org6981e66} +By definition of \(a\) being a unit, there exists \(ay = 1\) with \(y\) being an inverse of \(a\). +By multiplying our target \((y)ax = (y)b \Rightarrow x = yb\). + +To prove this is unique, assume that \(k\) and \(l\) are solutions of \(ax = b\). Then, \(ak = b\) and \(al = b\). Since \(a\) is a unit, by using our +previous strategy, \((y)ak = (y)b\) and \((y)al = (y)b\), so \(k = yb\) and \(l = yb\) and thus \(k = l\). + + +\section{Chapter 13} +\label{sec:org62ae8b0} +\subsection{A2} +\label{sec:org0b1499e} +As \(p | c \Rightarrow c = pk\), and \(p | c \Rightarrow c = ql\) then \(pk = ql\) and thus by Theorem 1.5 since \(p\) and \(q\) are prime \(p | l\) +or \(p | q\) and \(q | p\) or \(q | k\), but since \(p\) and \(q\) are prime, then it must be that only \(p | l\) and \(q | k\). + +Since \(p | l\) then \(l = mp\) and \(c = ql \Rightarrow c = qmp\) and \(qp\) is a factor of \(c\). + +\subsection{A3 (a)} +\label{sec:orge4f13f2} +GO = 0715 + +715\textsuperscript{3} (mod 2773) = 107 +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/alg_structures_assn_4.org b/Homework/math4310/alg_structures_assn_4.org new file mode 100644 index 0000000..cc35190 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_4.org @@ -0,0 +1,176 @@ +#+TITLE: Assignment Four +#+AUTHOR: Lizzy Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} +#+LATEX: \setlength\parindent{0pt} +#+OPTIONS: toc:nil + +* Section 3.1 +** Question One +*** a +$a \in R, b \in R \Rightarrow a + b \in R$ +*** b +$a \in R \Rightarow x \in R \ni a + x = 0_R$ +** Question Three +1. All operations are closed since only the elements in ${0, e, a, b}$ appear in the tables. +2. From the second row and columns in the multiplication table we see that $e$ is the multiplicative identity. +3. From the first row and columns in the addition table we see that $0$ is the zero element. +4. In this field, each element is its own additive inverse. +5. There is commutativity as the transpose of each table is identical to the original (symmetry along the diagonals). +** Question Six +*** a +Since our addition and multiplication operators are the same in $\mathds{Z}$, we have +associativity, commutativity, and distributivity. + +Sums of multiples of 3 are also multiples of 3: $3n + 3m = 3(n + m)$, so this set is closed under addition. + +Products of multiples of 3 are also multiples of 3: $(3n)(3m) = (3)(3nm)$, so this set is closed under multiplication. + +The additive inverse exists in the set for every element: $3n + x = 0 \Rightarrow x = 3 \cdot (-n)$. + +$0$ is the zero element and is a multiple of 3 since $3 \cdot 0 = 0$. + +Therefore ${x : x = 3n \ni n \in \mathds{Z}}$ is a subring of $\mathds{Z}$ + +*** b +Since our addition and multiplication operators are the same in $\mathds{Z}$, we have +associativity, commutativity, and distributivity. + +Sums of multiples of $k$ are also multiples of $k$: $kn + km = k(n + m)$, so this set is closed under addition. + +Products of multiples of $k$ are also multiples of $k$: $(kn)(km) = (k)(knm)$, so this set is closed under multiplication. + +The additive inverse exists exists in the set for every element: $kn + x = 0 \Rightarrow k = k \cdot (-n)$. + +$0$ is the zero element and is a multiple of k since $k \cdot 0 = 0$. + +Therefore ${x : x = kn \ni n \in \mathds{Z}}$ is a subring of $\mathds{Z}$ + +** Question Nine +*** a +${(0, 0), (1, 1), (2, 2), (3, 3), (4, 4), (5, 5)}$ +*** b +Since our addition and multiplication operators are the same as in $R$, then we have +associativity, commutativity, and distributivity. + +Sums of elements in $R*$ are also in $R*$ since any element $(r,r) \in R*, (j, j) \in R* = (r + j, r + j) \in R*$. + +Products of elements in $R*$ are also in $R*$ since any element $(r, r) \in R*, (j, j) \in R* = (rj, rj) \in R*$. + +The additive inverse exists in the set for every element: $(r, r) + x = 0 \Rightarrow x = (-r, -r) \in R*$. + +$(0, 0) \in R*$ is the zero element. + +Therefore ${(r, r) : (r, r) \in R*}$ is a subring of $R*$. + +** Question Ten +Consider $a \in S \ni a = (10, -10)$ and $b \in S \ni b = (10, -10)$, then $ab \notin S$ since +$ab = (100, 100)$ which does not follow the rule that $100 + 100 = 0$. +** Question Eleven +*** a +Addition is closed since +$\begin{smallmatrix} +a & a \\ +b & b +\end{smallmatrix}$ + $\begin{smallmatrix} +c & c \\ +d & d +\end{smallmatrix}$ = $\begin{smallmatrix} +(a + c) & (a + c) \\ +(b + d) & (b + d) +\end{smallmatrix}$ which of the form of the given rule. + +It is also closed under multiplication since +$\begin{smallmatrix} +a & a \\ +b & b +\end{smallmatrix}$ $\cdot$ $\begin{smallmatrix} +c & c \\ +d & d +\end{smallmatrix}$ = $\begin{smallmatrix} +(ac + ad) & (ac + ad) \\ +(bc + bd) & (bc + bd) +\end{smallmatrix}$ which is also of the form of the given rule. + +The zero element is the zero matrix $\begin{smallmatrix} +0 & 0 \\ +0 & 0 +\end{smallmatrix}$, trivially. + +Associativity and commutivity (of addition) come from these operations existing for 2x2 matrices in $M(\mathds{R})$. + +*** b +$\begin{smallmatrix} +a & a \\ +b & b +\end{smallmatrix}$ $\cdot$ $\begin{smallmatrix} +1 & 1 \\ +0 & 0 +\end{smallmatrix}$ = $\begin{smallmatrix} +(a(1) + a(0)) & (a(1) + a(0)) \\ +(b(1) + b(0)) & (b(1) + b(0)) +\end{smallmatrix}$ +which is equivalent to $\begin{smallmatrix} +a & a \\ +b & b +\end{smallmatrix}$ + +*** c +$\begin{smallmatrix} +1 & 1 \\ +0 & 0 +\end{smallmatrix}$ $\cdot$ $\begin{smallmatrix} +1 & 1 \\ +2 & 2 +\end{smallmatrix}$ = $\begin{smallmatrix} +((1)(1) + (1)(2)) & ((1)(1) + (1)(2)) \\ +((0)(1) + (0)(2)) & ((0)(1) + (0)(2)) +\end{smallmatrix}$ = $\begin{smallmatrix} +3 & 3 \\ +0 & 0 +\end{smallmatrix}$. +** Question Twelve +$\mathds{Z}[i]$ is closed under addition: $(a + bi) + (c + di) = (a + c) + (b + d)i$ and since +$\mathds{Z}$ is a ring itself, $(a + c) + (b + d)i$ is also in $\mathds{Z}[i]$. + +$\mathds{Z}[i]$ is closed under multiplication: $(a + bi) \cdot (c + di) = ac + adi + cbi + bdi^2 = (ac - bd) + (ad + bd)i$ +by similar logic. + +The additive inverse always exists in the set: $(a + bi) + x = 0 \Rightarrow x = -a - bi$. + +Finally, the zero element is trivially $0 + 0i$ since $(a + bi) + (0 + 0i) = a + bi$. + +** Question Fourteen +$S$ is closed under addition. For example given some $f, g \in S$ then $(f + g)(x) = h$ and $h$ will still satisfy the rule that +$h(2) = 0$ since $(f + g)(2) = f(2) + g(2) = 0 + 0$, and addition was already closed in the domain given that question 8 is a ring +itself. + +Similarly, $S$ is closed under multiplication. $(f \cdot g)(x) = h$ and h will still satisfy the rule as $h(2) = f(2) \cdot g(2) = 0 \cdot 0$. + +The zero element is $f \ni f(x) = 0$. + +Finally, the additive inverse $g$ exists in the set for each $f$ since $f + g = 0$ implies that $g$ is just $-f$ (the rule still +stands here). + +** Question Fifteen +*** b +| \odot | (0, 0) | (0, 1) | (0, 2) | (1, 0) | (1, 1) | (1, 2) | +| (0, 0) | (0, 0) | (0, 0) | (0, 0) | (0, 0) | (0, 0) | (0, 0) | +| (0, 1) | (0, 0) | (0, 1) | (0, 2) | (0, 0) | (0, 1) | (0, 2) | +| (0, 2) | (0, 0) | (0, 2) | (0, 1) | (0, 0) | (0, 2) | (0, 1) | +| (1, 0) | (0, 0) | (0, 0) | (0, 0) | (1, 0) | (1, 0) | (1, 0) | +| (1, 1) | (0, 0) | (0, 1) | (0, 2) | (1, 0) | (1, 1) | (1, 2) | +| (1, 2) | (0, 0) | (0, 2) | (0, 1) | (1, 0) | (1, 2) | (1, 1) | + +| \oplus | (0, 0) | (0, 1) | (0, 2) | (1, 0) | (1, 1) | (1, 2) | +| (0, 0) | (0, 0) | (0, 1) | (0, 2) | (1, 0) | (1, 1) | (1, 2) | +| (0, 1) | (0, 1) | (0, 2) | (0, 0) | (1, 1) | (1, 2) | (1, 0) | +| (0, 2) | (0, 2) | (0, 0) | (0, 1) | (1, 2) | (1, 0) | (1, 1) | +| (1, 0) | (1, 0) | (1, 1) | (1, 2) | (2, 0) | (2, 1) | (2, 2) | +| (1, 1) | (1, 1) | (1, 2) | (1, 0) | (2, 1) | (2, 2) | (2, 0) | +| (1, 2) | (1, 2) | (1, 0) | (1, 1) | (2, 2) | (2, 0) | (2, 1) | + +** Question Eighteen +No, by definition, as the distributive axiom is violated for this to be a ring. + +For example, $1(1 + 1) = (1)(1) + (1)(1) = 2$ but $1(1 + 1) = 1$. diff --git a/Homework/math4310/alg_structures_assn_4.pdf b/Homework/math4310/alg_structures_assn_4.pdf Binary files differnew file mode 100644 index 0000000..3e6a16d --- /dev/null +++ b/Homework/math4310/alg_structures_assn_4.pdf diff --git a/Homework/math4310/alg_structures_assn_4.tex b/Homework/math4310/alg_structures_assn_4.tex new file mode 100644 index 0000000..bf588dd --- /dev/null +++ b/Homework/math4310/alg_structures_assn_4.tex @@ -0,0 +1,233 @@ +% Created 2023-02-08 Wed 09:17 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} +\author{Lizzy Hunt} +\date{\today} +\title{Assignment Four} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Assignment Four}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Section 3.1} +\label{sec:org5ad4880} +\subsection{Question One} +\label{sec:org4dd5421} +\subsubsection{a} +\label{sec:orgfe8dc40} +\(a \in R, b \in R \Rightarrow a + b \in R\) +\subsubsection{b} +\label{sec:orgccbb819} +\(a \in R \Rightarow x \in R \ni a + x = 0_R\) +\subsection{Question Three} +\label{sec:orgc539ab7} +\begin{enumerate} +\item All operations are closed since only the elements in \({0, e, a, b}\) appear in the tables. +\item From the second row and columns in the multiplication table we see that \(e\) is the multiplicative identity. +\item From the first row and columns in the addition table we see that \(0\) is the zero element. +\item In this field, each element is its own additive inverse. +\item There is commutativity as the transpose of each table is identical to the original (symmetry along the diagonals). +\end{enumerate} +\subsection{Question Six} +\label{sec:orge1c7f2c} +\subsubsection{a} +\label{sec:orgb356ff9} +Since our addition and multiplication operators are the same in \(\mathds{Z}\), we have +associativity, commutativity, and distributivity. + +Sums of multiples of 3 are also multiples of 3: \(3n + 3m = 3(n + m)\), so this set is closed under addition. + +Products of multiples of 3 are also multiples of 3: \((3n)(3m) = (3)(3nm)\), so this set is closed under multiplication. + +The additive inverse exists in the set for every element: \(3n + x = 0 \Rightarrow x = 3 \cdot (-n)\). + +\(0\) is the zero element and is a multiple of 3 since \(3 \cdot 0 = 0\). + +Therefore \({x : x = 3n \ni n \in \mathds{Z}}\) is a subring of \(\mathds{Z}\) + +\subsubsection{b} +\label{sec:orga2b6add} +Since our addition and multiplication operators are the same in \(\mathds{Z}\), we have +associativity, commutativity, and distributivity. + +Sums of multiples of \(k\) are also multiples of \(k\): \(kn + km = k(n + m)\), so this set is closed under addition. + +Products of multiples of \(k\) are also multiples of \(k\): \((kn)(km) = (k)(knm)\), so this set is closed under multiplication. + +The additive inverse exists exists in the set for every element: \(kn + x = 0 \Rightarrow k = k \cdot (-n)\). + +\(0\) is the zero element and is a multiple of k since \(k \cdot 0 = 0\). + +Therefore \({x : x = kn \ni n \in \mathds{Z}}\) is a subring of \(\mathds{Z}\) + +\subsection{Question Nine} +\label{sec:org4f6749e} +\subsubsection{a} +\label{sec:orgc523c2e} +\({(0, 0), (1, 1), (2, 2), (3, 3), (4, 4), (5, 5)}\) +\subsubsection{b} +\label{sec:org970c88d} +Since our addition and multiplication operators are the same as in \(R\), then we have +associativity, commutativity, and distributivity. + +Sums of elements in \(R*\) are also in \(R*\) since any element \((r,r) \in R*, (j, j) \in R* = (r + j, r + j) \in R*\). + +Products of elements in \(R*\) are also in \(R*\) since any element \((r, r) \in R*, (j, j) \in R* = (rj, rj) \in R*\). + +The additive inverse exists in the set for every element: \((r, r) + x = 0 \Rightarrow x = (-r, -r) \in R*\). + +\((0, 0) \in R*\) is the zero element. + +Therefore \({(r, r) : (r, r) \in R*}\) is a subring of \(R*\). + +\subsection{Question Ten} +\label{sec:orgfdaf968} +Consider \(a \in S \ni a = (10, -10)\) and \(b \in S \ni b = (10, -10)\), then \(ab \notin S\) since +\(ab = (100, 100)\) which does not follow the rule that \(100 + 100 = 0\). +\subsection{Question Eleven} +\label{sec:org3b794ec} +\subsubsection{a} +\label{sec:orgef5a91b} +Addition is closed since +\(\begin{smallmatrix} +a & a \\ +b & b +\end{smallmatrix}\) + \(\begin{smallmatrix} +c & c \\ +d & d +\end{smallmatrix}\) = \(\begin{smallmatrix} +(a + c) & (a + c) \\ +(b + d) & (b + d) +\end{smallmatrix}\) which of the form of the given rule. + +It is also closed under multiplication since +\(\begin{smallmatrix} +a & a \\ +b & b +\end{smallmatrix}\) \(\cdot\) \(\begin{smallmatrix} +c & c \\ +d & d +\end{smallmatrix}\) = \(\begin{smallmatrix} +(ac + ad) & (ac + ad) \\ +(bc + bd) & (bc + bd) +\end{smallmatrix}\) which is also of the form of the given rule. + +The zero element is the zero matrix \(\begin{smallmatrix} +0 & 0 \\ +0 & 0 +\end{smallmatrix}\), trivially. + +Associativity and commutivity (of addition) come from these operations existing for 2x2 matrices in \(M(\mathds{R})\). + +\subsubsection{b} +\label{sec:orgb4b3acf} +\(\begin{smallmatrix} +a & a \\ +b & b +\end{smallmatrix}\) \(\cdot\) \(\begin{smallmatrix} +1 & 1 \\ +0 & 0 +\end{smallmatrix}\) = \(\begin{smallmatrix} +(a(1) + a(0)) & (a(1) + a(0)) \\ +(b(1) + b(0)) & (b(1) + b(0)) +\end{smallmatrix}\) +which is equivalent to \(\begin{smallmatrix} +a & a \\ +b & b +\end{smallmatrix}\) + +\subsubsection{c} +\label{sec:orga515fb6} +\(\begin{smallmatrix} +1 & 1 \\ +0 & 0 +\end{smallmatrix}\) \(\cdot\) \(\begin{smallmatrix} +1 & 1 \\ +2 & 2 +\end{smallmatrix}\) = \(\begin{smallmatrix} +((1)(1) + (1)(2)) & ((1)(1) + (1)(2)) \\ +((0)(1) + (0)(2)) & ((0)(1) + (0)(2)) +\end{smallmatrix}\) = \(\begin{smallmatrix} +3 & 3 \\ +0 & 0 +\end{smallmatrix}\). +\subsection{Question Twelve} +\label{sec:orgb1926b2} +\(\mathds{Z}[i]\) is closed under addition: \((a + bi) + (c + di) = (a + c) + (b + d)i\) and since +\(\mathds{Z}\) is a ring itself, \((a + c) + (b + d)i\) is also in \(\mathds{Z}[i]\). + +\(\mathds{Z}[i]\) is closed under multiplication: \((a + bi) \cdot (c + di) = ac + adi + cbi + bdi^2 = (ac - bd) + (ad + bd)i\) +by similar logic. + +The additive inverse always exists in the set: \((a + bi) + x = 0 \Rightarrow x = -a - bi\). + +Finally, the zero element is trivially \(0 + 0i\) since \((a + bi) + (0 + 0i) = a + bi\). + +\subsection{Question Fourteen} +\label{sec:org31f60fc} +The zero element is given as 2. + +\(S\) is closed under addition. For example given some \(f, g \in S\) then \((f + g)(x) = h\) and \(h\) will still satisfy the rule that +\(h(2) = 0\) since \((f + g)(2) = f(2) + g(2) = 0 + 0\), and addition was already closed in the domain given that question 8 is a ring +itself. + +Similarly, \(S\) is closed under multiplication. \((f \cdot g)(x) = h\) and h will still satisfy the rule as \(h(2) = f(2) \cdot g(2) = 0 \cdot 0\). + +The zero element is \(f \ni f(x) = 0\). + +Finally, the additive inverse \(g\) exists in the set for each \(f\) since \(f + g = 0\) implies that \(g\) is just \(-f\) (the rule still +stands here). + +\subsection{Question Fifteen} +\label{sec:org04d3ba1} +\subsubsection{b} +\label{sec:orgae94898} +\begin{center} +\begin{tabular}{lllllll} +\(\odot\) & (0, 0) & (0, 1) & (0, 2) & (1, 0) & (1, 1) & (1, 2)\\[0pt] +(0, 0) & (0, 0) & (0, 0) & (0, 0) & (0, 0) & (0, 0) & (0, 0)\\[0pt] +(0, 1) & (0, 0) & (0, 1) & (0, 2) & (0, 0) & (0, 1) & (0, 2)\\[0pt] +(0, 2) & (0, 0) & (0, 2) & (0, 1) & (0, 0) & (0, 2) & (0, 1)\\[0pt] +(1, 0) & (0, 0) & (0, 0) & (0, 0) & (1, 0) & (1, 0) & (1, 0)\\[0pt] +(1, 1) & (0, 0) & (0, 1) & (0, 2) & (1, 0) & (1, 1) & (1, 2)\\[0pt] +(1, 2) & (0, 0) & (0, 2) & (0, 1) & (1, 0) & (1, 2) & (1, 1)\\[0pt] +\end{tabular} +\end{center} + +\begin{center} +\begin{tabular}{lllllll} +\(\oplus\) & (0, 0) & (0, 1) & (0, 2) & (1, 0) & (1, 1) & (1, 2)\\[0pt] +(0, 0) & (0, 0) & (0, 1) & (0, 2) & (1, 0) & (1, 1) & (1, 2)\\[0pt] +(0, 1) & (0, 1) & (0, 2) & (0, 0) & (1, 1) & (1, 2) & (1, 0)\\[0pt] +(0, 2) & (0, 2) & (0, 0) & (0, 1) & (1, 2) & (1, 0) & (1, 1)\\[0pt] +(1, 0) & (1, 0) & (1, 1) & (1, 2) & (2, 0) & (2, 1) & (2, 2)\\[0pt] +(1, 1) & (1, 1) & (1, 2) & (1, 0) & (2, 1) & (2, 2) & (2, 0)\\[0pt] +(1, 2) & (1, 2) & (1, 0) & (1, 1) & (2, 2) & (2, 0) & (2, 1)\\[0pt] +\end{tabular} +\end{center} + +\subsection{Question Eighteen} +\label{sec:orga487be8} +No, by definition, as the distributive axiom is violated for this to be a ring. + +For example, \(1(1 + 1) = (1)(1) + (1)(1) = 2\) but \(1(1 + 1) = 1\). +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/alg_structures_assn_5.org b/Homework/math4310/alg_structures_assn_5.org new file mode 100644 index 0000000..78b0957 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_5.org @@ -0,0 +1,315 @@ +#+TITLE: Assignment Five +#+AUTHOR: Lizzy Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,landscape]{geometry} +#+LATEX: \setlength\parindent{0pt} +#+OPTIONS: toc:nil + +* Section 3.2 +** Question One +*** a +$a^2 - ab + ba - b^2$ +*** b +$a^3 + ba^2 + 2a^2b + 2ab^2 + ab^2 + b^3$ +*** c +(a) could be $a^2 - b^2$ + +(b) could be $a^3 + 3a^2b + 3ab^2 + b^3$ + +** Question Three +*** a +$\begin{smallmatrix} +0 & 0 \\ +0 & 0 \\ +\end{smallmatrix}$, $\begin{smallmatrix} +1 & 0 \\ +0 & 1 \\ +\end{smallmatrix}$, $\begin{smallmatrix} +1 & 0 & 0 \\ +0 & 1 & 0 \\ +0 & 0 & 1 \\ +\end{smallmatrix}$, $\begin{smallmatrix} +0 & 0 & 0 \\ +0 & 0 & 0 \\ +0 & 0 & 0 \\ +\end{smallmatrix}$ +*** b +\begin{verbatim} +>>> set(filter(lambda y: all([y**2 % 12 == y for x in range(12)]), range(12))) +{0, 1, 4, 9} +\end{verbatim} + +** Question Seven +S is closed under multiplication: +$i \in S, j \in S \Rightarrow i \cdot j = n1_R \cdot m1_R = (nm)1_R$. + +S is closed under subtraction: +$i \in S, j \in S \Rightarrow i - j = n1_R - m1_R = (n-m)1_R$ + +** Question Eight +Considering $n,m \in T$ then $n = xb, m = yb$ with $x,y \in R$: + +1. T is closed under multiplication: $n \cdot m = xb \cdot yb = (x \cdot y)b$, which follows the rule. +2. T is closed under subtraction: $n - m = xb - yb = (x - y)b$, which also follows the rule. + +We also know $T$ is not empty since it must have at least 0_R. + +** Question Ten +*** a +$\bar{R} = {(0, 0), (1, 0), (2, 0)}$ + +$\bar{S} = {(0, 0), (0, 1), (0, 2), (0, 3), (0, 4)}$ + +*** b +Considering $n, m \in \bar{R}$, then $n = (x, 0_S), n = (y, 0_S)$ with $x,y \in R$. + +1. $\bar{R}$ is closed under multiplication: $n \cdot m = (x, 0_S) \cdot (y, 0_S) = (x \cdot y, 0_S)$ and $x \cdot y \in R$, so thus $n \cdot m \in R \times S$. +2. $\bar{R}$ is closed under subtraction: $n - m = (x, 0_S) - (y, 0_S) = (x - y, 0_S)$ and $x - y \in R$, so thus $n - m \in R \times S$. + +We also know that $\bar{R}_0 = (0_R, 0_S) \in R \times S$ so $\bar{R}$ is not empty. + +*** c +Considering $n, m \in \bar{S}$, then $n = (0_R, x), n = (0_R, y)$ with $x,y \in S$. + +1. $\bar{S}$ is closed under multiplication: $n \cdot m = (0_R, x) \cdot (0_R, y) = (x \cdot y, 0_S)$ and $x \cdot y \in S$, so thus $n \cdot m \in R \times S$. +2. $\bar{S}$ is closed under subtraction: $n - m = (0_R, x) - (0_R, y) = (0_R, x - y)$ and $x - y \in R$, so thus $n - m \in R \times S$. + +We also know that $\bar{S}_0 = (0_R, 0_S) \in R \times S$ so $\bar{S}$ is not empty. + +** Question Thirteen +*** a +Considering $n, m \in S \cap T$, then $n \in S$ and $n \in T$, $m \in S$ and $m \in T$, therefore: + +1. $S \cap T$ is closed under multiplication as $m \cdot n$ must also be in $S \cap T$ +2. $S \cap T$ is closed under addition as $m + n$ must also be in $S \cap T$ + +Since $S$ and $T$ are both subrings of $R$, $0_R \in S \cap T$. + +*** b +No, consider $S$ being the integer multiples of 8 and $T$ being the integer multiples of 3 being subrings of $\mathds{Z}$ (proof of these being subrings is in +Question Six of Section 3.1 in Assignment Four), then $n \in S$ with $n = 8$ and $m \in T$ with $m = 3$ then $n + m = 11 \notin S \cup T$. + +** Question Fifteen - TODO + +** Question Twenty-One +*** a +From $ab = ac \Rightarrow ab - ac = 0_R \Rightarrow a(b - c) = 0_R$, we know $b-c$ is equivalent to $0_R$ since we're given that $a$ is a non-zero element. + +$b-c = 0_R \Rightarrow b = c$ + +*** b +From $ba = ca \Rightarrow ba - ca = 0_R \Rightarrow (b - c)(a) = 0_R$ we come to the same conclusion as (a) + +$b-c = 0_R \Rightarrow b = c$ + +* Section 3.3 +** Question One +In the true nature of being a computer science student, automate something for 2 hours that you could've done in 20 minutes! +#+BEGIN_SRC python :session "cct" :results none + cartesian_prod = lambda zn, zm: list([(i, j) for i in range(zn) for j in range(zm)]) + mult_tup = lambda a, b, zn, zm: ((a[0] * b[0]) % zn, (a[1] * b[1]) % zm) + add_tup = lambda a, b, zn, zm: ((a[0] + b[0]) % zn, (a[1] + b[1]) % zm) + empty_table = lambda col, row, symbol: [[symbol] + [str(x) for x in col]] + [[str(x)] + [0 for i in range(len(col))] for x in row] + + def make_cartesian_congruence_table(zn, zm, op, mapping, symbol): + cp = cartesian_prod(zn, zm) + mapped_cp = [cp[mapping[i]] for i in range(len(cp))] + table = empty_table(mapped_cp, mapped_cp, symbol) + for i in range(len(cp)): + for j in range(len(cp)): + table[i+1][j+1] = str(op(mapped_cp[i], mapped_cp[j], zn, zm)) + return table + + def make_normal_table(n, op, symbol): + table = empty_table(list(range(n)), list(range(n)), symbol) + for i in range(n): + for j in range(n): + table[i+1][j+1] = str(op(i, j) % n) + return table +#+END_SRC + +*** Z_2 \times Z_3 with bijection +#+BEGIN_SRC python :session "cct" :results none + bijection = [0, 4, 2, 3, 1, 5] +#+END_SRC + +**** Multiplication Tables +#+BEGIN_SRC python :session "cct" :results table + make_cartesian_congruence_table(2, 3, mult_tup, bijection, '\odot') +#+END_SRC + +| \odot | (0, 0) | (1, 1) | (0, 2) | (1, 0) | (0, 1) | (1, 2) | +| (0, 0) | (0, 0) | (0, 0) | (0, 0) | (0, 0) | (0, 0) | (0, 0) | +| (1, 1) | (0, 0) | (1, 1) | (0, 2) | (1, 0) | (0, 1) | (1, 2) | +| (0, 2) | (0, 0) | (0, 2) | (0, 1) | (0, 0) | (0, 2) | (0, 1) | +| (1, 0) | (0, 0) | (1, 0) | (0, 0) | (1, 0) | (0, 0) | (1, 0) | +| (0, 1) | (0, 0) | (0, 1) | (0, 2) | (0, 0) | (0, 1) | (0, 2) | +| (1, 2) | (0, 0) | (1, 2) | (0, 1) | (1, 0) | (0, 2) | (1, 1) | + +**** Addition Tables +#+BEGIN_SRC python :session "cct" :results table + make_cartesian_congruence_table(2, 3, add_tup, bijection, '\oplus') +#+END_SRC + +| \oplus | (0, 0) | (1, 1) | (0, 2) | (1, 0) | (0, 1) | (1, 2) | +| (0, 0) | (0, 0) | (1, 1) | (0, 2) | (1, 0) | (0, 1) | (1, 2) | +| (1, 1) | (1, 1) | (0, 2) | (1, 0) | (0, 1) | (1, 2) | (0, 0) | +| (0, 2) | (0, 2) | (1, 0) | (0, 1) | (1, 2) | (0, 0) | (1, 1) | +| (1, 0) | (1, 0) | (0, 1) | (1, 2) | (0, 0) | (1, 1) | (0, 2) | +| (0, 1) | (0, 1) | (1, 2) | (0, 0) | (1, 1) | (0, 2) | (1, 0) | +| (1, 2) | (1, 2) | (0, 0) | (1, 1) | (0, 2) | (1, 0) | (0, 1) | + +*** Z_6 +**** Multiplication Tables +#+BEGIN_SRC python :session "cct" :results table + make_normal_table(6, lambda a, b: a * b, '\odot') +#+END_SRC + +| \odot | 0 | 1 | 2 | 3 | 4 | 5 | +| 0 | 0 | 0 | 0 | 0 | 0 | 0 | +| 1 | 0 | 1 | 2 | 3 | 4 | 5 | +| 2 | 0 | 2 | 4 | 0 | 2 | 4 | +| 3 | 0 | 3 | 0 | 3 | 0 | 3 | +| 4 | 0 | 4 | 2 | 0 | 4 | 2 | +| 5 | 0 | 5 | 4 | 3 | 2 | 1 | + +**** Addition Tables +#+BEGIN_SRC python :session "cct" :results table + make_normal_table(6, lambda a, b: a + b, '\oplus') +#+END_SRC + +| \oplus | 0 | 1 | 2 | 3 | 4 | 5 | +| 0 | 0 | 1 | 2 | 3 | 4 | 5 | +| 1 | 1 | 2 | 3 | 4 | 5 | 0 | +| 2 | 2 | 3 | 4 | 5 | 0 | 1 | +| 3 | 3 | 4 | 5 | 0 | 1 | 2 | +| 4 | 4 | 5 | 0 | 1 | 2 | 3 | +| 5 | 5 | 0 | 1 | 2 | 3 | 4 | + +** Question Two +#+BEGIN_SRC python :session "cct" :results table + bijection = [0, 3, 2, 1] + make_cartesian_congruence_table(2, 2, mult_tup, bijection, '\odot') +#+END_SRC + +| \odot | (0, 0) | (1, 1) | (1, 0) | (0, 1) | +| (0, 0) | (0, 0) | (0, 0) | (0, 0) | (0, 0) | +| (1, 1) | (0, 0) | (1, 1) | (1, 0) | (0, 1) | +| (1, 0) | (0, 0) | (1, 0) | (1, 0) | (0, 0) | +| (0, 1) | (0, 0) | (0, 1) | (0, 0) | (0, 1) | + +#+BEGIN_SRC python :session "cct" :results table + bijection = [0, 3, 2, 1] + make_cartesian_congruence_table(2, 2, add_tup, bijection, '\oplus') +#+END_SRC + +| \oplus | (0, 0) | (1, 1) | (1, 0) | (0, 1) | +| (0, 0) | (0, 0) | (1, 1) | (1, 0) | (0, 1) | +| (1, 1) | (1, 1) | (0, 0) | (0, 1) | (1, 0) | +| (1, 0) | (1, 0) | (0, 1) | (0, 0) | (1, 1) | +| (0, 1) | (0, 1) | (1, 0) | (1, 1) | (0, 0) | + +** Question Three +1. $f$ is injective, since $f(a) = f(b) \Rightarrow (a,a) = (b,b) \Rightarrow a = b$ +2. $f$ is surjective since every range element in $R^*$, $(a,a)$ is mapped to $a \in R$ by definition +3. $f(a) + f(b) = (a, a) + (b, b) = (a + b, a + b) = f(a + b)$ and $f(a)f(b) = (a, a) \cdot (b, b) = (ab, ab) = f(ab)$ + +** Question Four +$f(1)f(3) = (2)(6) \equiv_{10} 2$ but $f(3) = 6$ which doesn't hold the properties of homomorphism. + +** Question Five +Consider the given function: +1. $f$ is injective, since $f(a) = f(b) \Rightarrow$ $\begin{smallmatrix} 0 & 0 \\ 0 & a \end{smallmatrix}$ = $\begin{smallmatrix} 0 & 0 \\ 0 & b \end{smallmatrix}$ $\Rightarrow a = b$ +2. $f$ is surjective, since every range element $\begin{smallmatrix} 0 & 0 \\ 0 & a \end{smallmatrix}$ has an element in $\mathds{R}$, $a$, such that $f(a) =$ $\begin{smallmatrix} 0 & 0 \\ 0 & a \end{smallmatrix}$ by definition +3. $f(a) + f(b) =$ $\begin{smallmatrix} 0 & 0 \\ 0 & a \end{smallmatrix}$ + $\begin{smallmatrix} 0 & 0 \\ 0 & b \end{smallmatrix}$ = $\begin{smallmatrix} 0 & 0 \\ 0 & (a + b) \end{smallmatrix}$ = $f(a + b)$, + and $f(a) \cdot f(b) =$ $\begin{smallmatrix} 0 & 0 \\ 0 & a \end{smallmatrix}$ \cdot $\begin{smallmatrix} 0 & 0 \\ 0 & b \end{smallmatrix}$ = $\begin{smallmatrix} 0 & 0 \\ 0 & (a \cdot b) \end{smallmatrix}$ = $f(a \cdot b)$, + +** Question Nine - TODO + +** Question Eleven +*** b +\begin{verbatim} +>>> f = lambda x: 3 * x +>>> list(filter(lambda x: f(x * x) != (f(x) * f(x)), range(0, 20, 2))) +[2, 4, 6, 8, 10, 12, 14, 16, 18] +\end{verbatim} +*** d +\begin{verbatim} +>>> k = lambda x: 0 if x == 0 else (x ** -1) +>>> list(filter(lambda x: k(x * x) != (k(x) * k(x)), range(0, 20))) +[5, 10, 13, 19] +\end{verbatim} +** Question Twelve +*** c +Not a homomorphism. Just from reducing $f(x + x)$ we find $f(x + x) \neq f(x) + f(x)$: + +\begin{equation*} +f(x + x) = \dfrac{1}{(x + x)^2 + 1} = \dfrac{1}{4x^2 + 1} +\end{equation*} + +\begin{equation*} +f(x) + f(x) = \dfrac{1}{x^2 + 1} + \dfrac{1}{x^2 + 1} = \dfrac{2}{x^2 + 1} +\end{equation*} + +Thus $f(x + x) \neq f(x) + f(x)$. +*** d +\begin{verbatim} +>>> import numpy as np +>>> h = lambda x: [[-x, 0], [x, 0]] +>>> list(filter(lambda x: not np.array_equiv(h(x * x), np.dot(h(x), h(x))), range(0, 20)) +[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19] +\end{verbatim} +** Question Thirteen +*** a +If $r \in R$ then $(r, 0_S) \in R \times S$, and $f((r, 0_S)) = r$, so every range element has a domain element mapping to it. + +For some $a = (r, m) \in R \times S$ and $b = (t, v) \in R \times S$ then $f((r, m)) + f((t, v)) = r + t = f((r + t, v + m))$, and +$f((r, m)) \cdot f((t, v)) = r \cdot t = f((r \cdot t, v \cdot m))$. + +*** b +If $s \in S$ then $(0_R, s) \in R \times S$, and $f((0_R, s)) = s$, so every range element has a domain element mapping to it. + +For some $a = (r, m) \in R \times S$ and $b = (t, v) \in R \times S$ then $f((r, m)) + f((t, v)) = m + v = f((r + t, m + v))$, and +$f((r, m)) \cdot f((t, v)) = m \cdot v = f((r \cdot t, m \cdot v))$. + +** Question Fifteen +Consider $f: Z_4 \rightarrow Z_4 \ni f(x) = 0$, then 2 is a zero divisor, but 0 is not by definition. + +** Question Twenty One +*** Lemma +We assume a multiplicative identity $x$ exists in $\mathds{Z}^{*}$: + +$b \odot x = b \Rightarrow b + x - bx = b \Rightarrow x - bx = 0 \Rightarrow x(1-b) = 0$ and $1-b \neq 0 \forall b \in \mathds{Z}^{*}$ so $x = 0$. + +which is verified by: + +$0 \odot b = 0 + b - 0 \cdot b = b$ and $b \odot 0 = b + 0 - b \cdot 0 = b$. + +*** Proof + +Consider $f : \mathds{Z}^{} \rightarrow \mathds{Z}^{*}$ to be the isomorphism we so desire, then by Theorem 3.10, +f(1 \in \mathds{Z}) = 0 \in \mathds{Z}^{*}. + +Therefore, f(2) = f(1 + 1) = f(1) \oplus f(1) = -1, f(3) = f(2 + 1) = -1 \oplus f(1) = -2. + +$f : \mathds{Z}^{} \rightarrow \mathds{Z}^{*} \ni f(x) = 1 - x$ seems to fit the bill nicely. + +1. $f$ is a bijection since we have an inverse $x = 1 - f(x)$ +2. $f(a \oplus b) = 1 - (a \oplus b) = 1 - (a + b - 1) = (1 - a) + (1 - b) = f(a) + f(b)$ and + $f(a \odot b) = 1 - (a \odot b) = 1 - (a + b - ab) = (1-a) \cdot (1-b) = f(a) \cdot f(b)$ + +** Question Twenty Four +*** a +1. By the usual coordinate addition we know that $a, b \in R \Rightarrow a + b \in R$ and is associative, commutative, and the additive identity is $(0, 0)$. +2. $R$ is closed under multiplication: $a, b \in R \Rightarrow a = (c, d) \wedge b = (e, f) \Rightarrow a \cdot b = (ce, de)$ and since $c, d, e, f \in \mathds{R}$ then $(ce, de) \in \mathds{R} \times \mathds{R}$ by definition. +3. Multiplication is associative: $a, b, c \in R \Rightarrow a = (d, e) \wedge b = (f, g) \wedge c = (h, i) \Rightarrow (a \cdot b) \cdot c = (df, ef) \cdot (h, i) = (dfh, efh)$ and $a \cdot (b \cdot c) = (d, e) \cdot (fh, gh) = (dfh, efh)$ +4. Multiplication is distributive: $a, b, c \in R \Rightarrow a = (d, e) \wedge b = (f, g) \wedge c = (h, i) \Rightarrow a(b + c) = (e, f) \cdot (f + h, g + i) = (ef + eh, ff + fh) = (ef, ff) + (eh, fh) = a \cdot b + a \cdot c$ + and $a, b, c \in R \Rightarrow a = (d, e) \wedge b = (f, g) \wedge c = (h, i) \Rightarrow (a + b) \cdot c = (d + f, e + g) \cdot (h, i) = (dh + fh, eh + gh) = (dh, eh) + (fh, gh) = a \cdot c + b \cdot c$ +*** b +Consider the function $f: R \rightarrow M(\mathds{R})$ is an isomorphism, such that $f((a, b)) =$ $\begin{smallmatrix} a & 0 \\ b & 0 \end{smallmatrix}$, then: +1. $f$ is surjective since every element in the range has a domain element $\begin{smallmatrix} a & 0 \\ b & 0 \end{smallmatrix} = y \ni f((a, b)) = y$ +2. $f$ is injective since $f((c, d) = x) = f((e, f) = y) \Rightarrow$ $\begin{smallmatrix} c & 0 \\ d & 0 \end{smallmatrix}$ = $\begin{smallmatrix} e & 0 \\ f & 0 \end{smallmatrix}$ $\Rightarrow c = e \wedge d = f \Rightarrow x = y$ +3. $f((c, d) = x) + f((e, f) = y) \Rightarrow$ $\begin{smallmatrix} c & 0 \\ d & 0 \end{smallmatrix}$ + $\begin{smallmatrix} e & 0 \\ f & 0 \end{smallmatrix}$ = $\begin{smallmatrix} c + e & 0 \\ d + f & 0 \end{smallmatrix}$ + $= f(x + y)$, and $f((c, d) = x) \cdot f((e, f) = y) \Rightarrow$ $\begin{smallmatrix} c & 0 \\ d & 0 \end{smallmatrix}$ $\cdot$ $\begin{smallmatrix} e & 0 \\ f & 0 \end{smallmatrix}$ = $\begin{smallmatrix} ce & 0 \\ de & 0 \end{smallmatrix}$ + $= f(x \cdot y)$ + diff --git a/Homework/math4310/alg_structures_assn_5.pdf b/Homework/math4310/alg_structures_assn_5.pdf Binary files differnew file mode 100644 index 0000000..23f8ee7 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_5.pdf diff --git a/Homework/math4310/alg_structures_assn_5.tex b/Homework/math4310/alg_structures_assn_5.tex new file mode 100644 index 0000000..1cdb649 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_5.tex @@ -0,0 +1,434 @@ +% Created 2023-02-17 Fri 12:59 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,landscape]{geometry} +\author{Lizzy Hunt} +\date{\today} +\title{Assignment Five} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Assignment Five}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Section 3.2} +\label{sec:org258154b} +\subsection{Question One} +\label{sec:orgf02bb85} +\subsubsection{a} +\label{sec:orgccb1c0c} +\(a^2 - ab + ba - b^2\) +\subsubsection{b} +\label{sec:org9164b85} +\(a^3 + ba^2 + 2a^2b + 2ab^2 + ab^2 + b^3\) +\subsubsection{c} +\label{sec:orgdaba485} +(a) could be \(a^2 - b^2\) + +(b) could be \(a^3 + 3a^2b + 3ab^2 + b^3\) + +\subsection{Question Three} +\label{sec:org4d02a16} +\subsubsection{a} +\label{sec:orgb743fca} +\(\begin{smallmatrix} +0 & 0 \\ +0 & 0 \\ +\end{smallmatrix}\), \(\begin{smallmatrix} +1 & 0 \\ +0 & 1 \\ +\end{smallmatrix}\), \(\begin{smallmatrix} +1 & 0 & 0 \\ +0 & 1 & 0 \\ +0 & 0 & 1 \\ +\end{smallmatrix}\), \(\begin{smallmatrix} +0 & 0 & 0 \\ +0 & 0 & 0 \\ +0 & 0 & 0 \\ +\end{smallmatrix}\) +\subsubsection{b} +\label{sec:org8300d7e} +\begin{verbatim} +>>> set(filter(lambda y: all([y**2 % 12 == y for x in range(12)]), range(12))) +{0, 1, 4, 9} +\end{verbatim} + +\subsection{Question Seven} +\label{sec:org9152891} +S is closed under multiplication: +\(i \in S, j \in S \Rightarrow i \cdot j = n1_R \cdot m1_R = (nm)1_R\). + +S is closed under subtraction: +\(i \in S, j \in S \Rightarrow i - j = n1_R - m1_R = (n-m)1_R\) + +\subsection{Question Eight} +\label{sec:org3ed31b0} +Considering \(n,m \in T\) then \(n = xb, m = yb\) with \(x,y \in R\): + +\begin{enumerate} +\item T is closed under multiplication: \(n \cdot m = xb \cdot yb = (x \cdot y)b\), which follows the rule. +\item T is closed under subtraction: \(n - m = xb - yb = (x - y)b\), which also follows the rule. +\end{enumerate} + +We also know \(T\) is not empty since it must have at least 0\textsubscript{R}. + +\subsection{Question Ten} +\label{sec:orgc4efb36} +\subsubsection{a} +\label{sec:orgbc2ab9d} +\(\bar{R} = {(0, 0), (1, 0), (2, 0)}\) + +\(\bar{S} = {(0, 0), (0, 1), (0, 2), (0, 3), (0, 4)}\) + +\subsubsection{b} +\label{sec:org564675e} +Considering \(n, m \in \bar{R}\), then \(n = (x, 0_S), n = (y, 0_S)\) with \(x,y \in R\). + +\begin{enumerate} +\item \(\bar{R}\) is closed under multiplication: \(n \cdot m = (x, 0_S) \cdot (y, 0_S) = (x \cdot y, 0_S)\) and \(x \cdot y \in R\), so thus \(n \cdot m \in R \times S\). +\item \(\bar{R}\) is closed under subtraction: \(n - m = (x, 0_S) - (y, 0_S) = (x - y, 0_S)\) and \(x - y \in R\), so thus \(n - m \in R \times S\). +\end{enumerate} + +We also know that \(\bar{R}_0 = (0_R, 0_S) \in R \times S\) so \(\bar{R}\) is not empty. + +\subsubsection{c} +\label{sec:org5905763} +Considering \(n, m \in \bar{S}\), then \(n = (0_R, x), n = (0_R, y)\) with \(x,y \in S\). + +\begin{enumerate} +\item \(\bar{S}\) is closed under multiplication: \(n \cdot m = (0_R, x) \cdot (0_R, y) = (x \cdot y, 0_S)\) and \(x \cdot y \in S\), so thus \(n \cdot m \in R \times S\). +\item \(\bar{S}\) is closed under subtraction: \(n - m = (0_R, x) - (0_R, y) = (0_R, x - y)\) and \(x - y \in R\), so thus \(n - m \in R \times S\). +\end{enumerate} + +We also know that \(\bar{S}_0 = (0_R, 0_S) \in R \times S\) so \(\bar{S}\) is not empty. + +\subsection{Question Thirteen} +\label{sec:orgfc1192c} +\subsubsection{a} +\label{sec:orgdc9f5c9} +Considering \(n, m \in S \cap T\), then \(n \in S\) and \(n \in T\), \(m \in S\) and \(m \in T\), therefore: + +\begin{enumerate} +\item \(S \cap T\) is closed under multiplication as \(m \cdot n\) must also be in \(S \cap T\) +\item \(S \cap T\) is closed under addition as \(m + n\) must also be in \(S \cap T\) +\end{enumerate} + +Since \(S\) and \(T\) are both subrings of \(R\), \(0_R \in S \cap T\). + +\subsubsection{b} +\label{sec:orgeb2e7d6} +No, consider \(S\) being the integer multiples of 8 and \(T\) being the integer multiples of 3 being subrings of \(\mathds{Z}\) (proof of these being subrings is in +Question Six of Section 3.1 in Assignment Four), then \(n \in S\) with \(n = 8\) and \(m \in T\) with \(m = 3\) then \(n + m = 11 \notin S \cup T\). + +\subsection{Question Fifteen - TODO} +\label{sec:org675f8a8} + +\subsection{Question Twenty-One} +\label{sec:org0c713ff} +\subsubsection{a} +\label{sec:org6158430} +From \(ab = ac \Rightarrow ab - ac = 0_R \Rightarrow a(b - c) = 0_R\), we know \(b-c\) is equivalent to \(0_R\) since we're given that \(a\) is a non-zero element. + +\(b-c = 0_R \Rightarrow b = c\) + +\subsubsection{b} +\label{sec:org4391edc} +From \(ba = ca \Rightarrow ba - ca = 0_R \Rightarrow (b - c)(a) = 0_R\) we come to the same conclusion as (a) + +\(b-c = 0_R \Rightarrow b = c\) + +\section{Section 3.3} +\label{sec:orgff5f7f5} +\subsection{Question One} +\label{sec:org08aff62} +In the true nature of being a computer science student, automate something for 2 hours that you could've done in 20 minutes! +\begin{verbatim} +cartesian_prod = lambda zn, zm: list([(i, j) for i in range(zn) for j in range(zm)]) +mult_tup = lambda a, b, zn, zm: ((a[0] * b[0]) % zn, (a[1] * b[1]) % zm) +add_tup = lambda a, b, zn, zm: ((a[0] + b[0]) % zn, (a[1] + b[1]) % zm) +empty_table = lambda col, row, symbol: [[symbol] + [str(x) for x in col]] + [[str(x)] + [0 for i in range(len(col))] for x in row] + +def make_cartesian_congruence_table(zn, zm, op, mapping, symbol): + cp = cartesian_prod(zn, zm) + mapped_cp = [cp[mapping[i]] for i in range(len(cp))] + table = empty_table(mapped_cp, mapped_cp, symbol) + for i in range(len(cp)): + for j in range(len(cp)): + table[i+1][j+1] = str(op(mapped_cp[i], mapped_cp[j], zn, zm)) + return table + +def make_normal_table(n, op, symbol): + table = empty_table(list(range(n)), list(range(n)), symbol) + for i in range(n): + for j in range(n): + table[i+1][j+1] = str(op(i, j) % n) + return table +\end{verbatim} + +\subsubsection{Z\textsubscript{2} \texttimes{} Z\textsubscript{3} with bijection} +\label{sec:orgcac27c3} +\begin{verbatim} +bijection = [0, 4, 2, 3, 1, 5] +\end{verbatim} + +\begin{enumerate} +\item Multiplication Tables +\label{sec:org1f4aa9f} +\begin{verbatim} +make_cartesian_congruence_table(2, 3, mult_tup, bijection, '\odot') +\end{verbatim} + +\begin{center} +\begin{tabular}{lllllll} +\(\odot\) & (0, 0) & (1, 1) & (0, 2) & (1, 0) & (0, 1) & (1, 2)\\[0pt] +(0, 0) & (0, 0) & (0, 0) & (0, 0) & (0, 0) & (0, 0) & (0, 0)\\[0pt] +(1, 1) & (0, 0) & (1, 1) & (0, 2) & (1, 0) & (0, 1) & (1, 2)\\[0pt] +(0, 2) & (0, 0) & (0, 2) & (0, 1) & (0, 0) & (0, 2) & (0, 1)\\[0pt] +(1, 0) & (0, 0) & (1, 0) & (0, 0) & (1, 0) & (0, 0) & (1, 0)\\[0pt] +(0, 1) & (0, 0) & (0, 1) & (0, 2) & (0, 0) & (0, 1) & (0, 2)\\[0pt] +(1, 2) & (0, 0) & (1, 2) & (0, 1) & (1, 0) & (0, 2) & (1, 1)\\[0pt] +\end{tabular} +\end{center} + +\item Addition Tables +\label{sec:org807c598} +\begin{verbatim} +make_cartesian_congruence_table(2, 3, add_tup, bijection, '\oplus') +\end{verbatim} + +\begin{center} +\begin{tabular}{lllllll} +\(\oplus\) & (0, 0) & (1, 1) & (0, 2) & (1, 0) & (0, 1) & (1, 2)\\[0pt] +(0, 0) & (0, 0) & (1, 1) & (0, 2) & (1, 0) & (0, 1) & (1, 2)\\[0pt] +(1, 1) & (1, 1) & (0, 2) & (1, 0) & (0, 1) & (1, 2) & (0, 0)\\[0pt] +(0, 2) & (0, 2) & (1, 0) & (0, 1) & (1, 2) & (0, 0) & (1, 1)\\[0pt] +(1, 0) & (1, 0) & (0, 1) & (1, 2) & (0, 0) & (1, 1) & (0, 2)\\[0pt] +(0, 1) & (0, 1) & (1, 2) & (0, 0) & (1, 1) & (0, 2) & (1, 0)\\[0pt] +(1, 2) & (1, 2) & (0, 0) & (1, 1) & (0, 2) & (1, 0) & (0, 1)\\[0pt] +\end{tabular} +\end{center} +\end{enumerate} + +\subsubsection{Z\textsubscript{6}} +\label{sec:orgbe8adf1} +\begin{enumerate} +\item Multiplication Tables +\label{sec:orga98b12b} +\begin{verbatim} +make_normal_table(6, lambda a, b: a * b, '\odot') +\end{verbatim} + +\begin{center} +\begin{tabular}{rrrrrrr} +\(\odot\) & 0 & 1 & 2 & 3 & 4 & 5\\[0pt] +0 & 0 & 0 & 0 & 0 & 0 & 0\\[0pt] +1 & 0 & 1 & 2 & 3 & 4 & 5\\[0pt] +2 & 0 & 2 & 4 & 0 & 2 & 4\\[0pt] +3 & 0 & 3 & 0 & 3 & 0 & 3\\[0pt] +4 & 0 & 4 & 2 & 0 & 4 & 2\\[0pt] +5 & 0 & 5 & 4 & 3 & 2 & 1\\[0pt] +\end{tabular} +\end{center} + +\item Addition Tables +\label{sec:orgfcf7bde} +\begin{verbatim} +make_normal_table(6, lambda a, b: a + b, '\oplus') +\end{verbatim} + +\begin{center} +\begin{tabular}{rrrrrrr} +\(\oplus\) & 0 & 1 & 2 & 3 & 4 & 5\\[0pt] +0 & 0 & 1 & 2 & 3 & 4 & 5\\[0pt] +1 & 1 & 2 & 3 & 4 & 5 & 0\\[0pt] +2 & 2 & 3 & 4 & 5 & 0 & 1\\[0pt] +3 & 3 & 4 & 5 & 0 & 1 & 2\\[0pt] +4 & 4 & 5 & 0 & 1 & 2 & 3\\[0pt] +5 & 5 & 0 & 1 & 2 & 3 & 4\\[0pt] +\end{tabular} +\end{center} +\end{enumerate} + +\subsection{Question Two} +\label{sec:org9540aed} +\begin{verbatim} +bijection = [0, 3, 2, 1] +make_cartesian_congruence_table(2, 2, mult_tup, bijection, '\odot') +\end{verbatim} + +\begin{center} +\begin{tabular}{lllll} +\(\odot\) & (0, 0) & (1, 1) & (1, 0) & (0, 1)\\[0pt] +(0, 0) & (0, 0) & (0, 0) & (0, 0) & (0, 0)\\[0pt] +(1, 1) & (0, 0) & (1, 1) & (1, 0) & (0, 1)\\[0pt] +(1, 0) & (0, 0) & (1, 0) & (1, 0) & (0, 0)\\[0pt] +(0, 1) & (0, 0) & (0, 1) & (0, 0) & (0, 1)\\[0pt] +\end{tabular} +\end{center} + +\begin{verbatim} +bijection = [0, 3, 2, 1] +make_cartesian_congruence_table(2, 2, add_tup, bijection, '\oplus') +\end{verbatim} + +\begin{center} +\begin{tabular}{lllll} +\(\oplus\) & (0, 0) & (1, 1) & (1, 0) & (0, 1)\\[0pt] +(0, 0) & (0, 0) & (1, 1) & (1, 0) & (0, 1)\\[0pt] +(1, 1) & (1, 1) & (0, 0) & (0, 1) & (1, 0)\\[0pt] +(1, 0) & (1, 0) & (0, 1) & (0, 0) & (1, 1)\\[0pt] +(0, 1) & (0, 1) & (1, 0) & (1, 1) & (0, 0)\\[0pt] +\end{tabular} +\end{center} + +\subsection{Question Three} +\label{sec:org421e770} +\begin{enumerate} +\item \(f\) is injective, since \(f(a) = f(b) \Rightarrow (a,a) = (b,b) \Rightarrow a = b\) +\item \(f\) is surjective since every range element in \(R^*\), \((a,a)\) is mapped to \(a \in R\) by definition +\item \(f(a) + f(b) = (a, a) + (b, b) = (a + b, a + b) = f(a + b)\) and \(f(a)f(b) = (a, a) \cdot (b, b) = (ab, ab) = f(ab)\) +\end{enumerate} + +\subsection{Question Four} +\label{sec:org1f8479a} +\(f(1)f(3) = (2)(6) \equiv_{10} 2\) but \(f(3) = 6\) which doesn't hold the properties of homomorphism. + +\subsection{Question Five} +\label{sec:orgeb656c3} +Consider the given function: +\begin{enumerate} +\item \(f\) is injective, since \(f(a) = f(b) \Rightarrow\) \(\begin{smallmatrix} 0 & 0 \\ 0 & a \end{smallmatrix}\) = \(\begin{smallmatrix} 0 & 0 \\ 0 & b \end{smallmatrix}\) \(\Rightarrow a = b\) +\item \(f\) is surjective, since every range element \(\begin{smallmatrix} 0 & 0 \\ 0 & a \end{smallmatrix}\) has an element in \(\mathds{R}\), \(a\), such that \(f(a) =\) \(\begin{smallmatrix} 0 & 0 \\ 0 & a \end{smallmatrix}\) by definition +\item \(f(a) + f(b) =\) \(\begin{smallmatrix} 0 & 0 \\ 0 & a \end{smallmatrix}\) + \(\begin{smallmatrix} 0 & 0 \\ 0 & b \end{smallmatrix}\) = \(\begin{smallmatrix} 0 & 0 \\ 0 & (a + b) \end{smallmatrix}\) = \(f(a + b)\), +and \(f(a) \cdot f(b) =\) \(\begin{smallmatrix} 0 & 0 \\ 0 & a \end{smallmatrix}\) \(\cdot\) \(\begin{smallmatrix} 0 & 0 \\ 0 & b \end{smallmatrix}\) = \(\begin{smallmatrix} 0 & 0 \\ 0 & (a \cdot b) \end{smallmatrix}\) = \(f(a \cdot b)\), +\end{enumerate} + +\subsection{Question Nine - TODO} +\label{sec:org2f29e8e} + +\subsection{Question Eleven} +\label{sec:org3e455ed} +\subsubsection{b} +\label{sec:org24734c1} +\begin{verbatim} +>>> f = lambda x: 3 * x +>>> list(filter(lambda x: f(x * x) != (f(x) * f(x)), range(0, 20, 2))) +[2, 4, 6, 8, 10, 12, 14, 16, 18] +\end{verbatim} +\subsubsection{d} +\label{sec:orgc2ba394} +\begin{verbatim} +>>> k = lambda x: 0 if x == 0 else (x ** -1) +>>> list(filter(lambda x: k(x * x) != (k(x) * k(x)), range(0, 20))) +[5, 10, 13, 19] +\end{verbatim} +\subsection{Question Twelve} +\label{sec:org95ce95e} +\subsubsection{c} +\label{sec:org77d2e96} +Not a homomorphism. Just from reducing \(f(x + x)\) we find \(f(x + x) \neq f(x) + f(x)\): + +\begin{equation*} +f(x + x) = \dfrac{1}{(x + x)^2 + 1} = \dfrac{1}{4x^2 + 1} +\end{equation*} + +\begin{equation*} +f(x) + f(x) = \dfrac{1}{x^2 + 1} + \dfrac{1}{x^2 + 1} = \dfrac{2}{x^2 + 1} +\end{equation*} + +Thus \(f(x + x) \neq f(x) + f(x)\). +\subsubsection{d} +\label{sec:org1c2b201} +\begin{verbatim} +>>> import numpy as np +>>> h = lambda x: [[-x, 0], [x, 0]] +>>> list(filter(lambda x: not np.array_equiv(h(x * x), np.dot(h(x), h(x))), range(0, 20)) +[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19] +\end{verbatim} +\subsection{Question Thirteen} +\label{sec:org57e2c18} +\subsubsection{a} +\label{sec:org7515001} +If \(r \in R\) then \((r, 0_S) \in R \times S\), and \(f((r, 0_S)) = r\), so every range element has a domain element mapping to it. + +For some \(a = (r, m) \in R \times S\) and \(b = (t, v) \in R \times S\) then \(f((r, m)) + f((t, v)) = r + t = f((r + t, v + m))\), and +\(f((r, m)) \cdot f((t, v)) = r \cdot t = f((r \cdot t, v \cdot m))\). + +\subsubsection{b} +\label{sec:orgfb2a3ab} +If \(s \in S\) then \((0_R, s) \in R \times S\), and \(f((0_R, s)) = s\), so every range element has a domain element mapping to it. + +For some \(a = (r, m) \in R \times S\) and \(b = (t, v) \in R \times S\) then \(f((r, m)) + f((t, v)) = m + v = f((r + t, m + v))\), and +\(f((r, m)) \cdot f((t, v)) = m \cdot v = f((r \cdot t, m \cdot v))\). + +\subsection{Question Fifteen} +\label{sec:org4046d12} +Consider \(f: Z_4 \rightarrow Z_4 \ni f(x) = 0\), then 2 is a zero divisor, but 0 is not by definition. + +\subsection{Question Twenty One} +\label{sec:org48d8cc7} +\subsubsection{Lemma} +\label{sec:org3598e64} +We assume a multiplicative identity \(x\) exists in \(\mathds{Z}^{*}\): + +\(b \odot x = b \Rightarrow b + x - bx = b \Rightarrow x - bx = 0 \Rightarrow x(1-b) = 0\) and \(1-b \neq 0 \forall b \in \mathds{Z}^{*}\) so \(x = 0\). + +which is verified by: + +\(0 \odot b = 0 + b - 0 \cdot b = b\) and \(b \odot 0 = b + 0 - b \cdot 0 = b\). + +\subsubsection{Proof} +\label{sec:orgee74248} + +Consider \(f : \mathds{Z}^{} \rightarrow \mathds{Z}^{*}\) to be the isomorphism we so desire, then by Theorem 3.10, +f(1 \(\in\) \mathds{Z}) = 0 \(\in\) \mathds{Z}\textsuperscript{*}. + +Therefore, f(2) = f(1 + 1) = f(1) \(\oplus\) f(1) = -1, f(3) = f(2 + 1) = -1 \(\oplus\) f(1) = -2. + +\(f : \mathds{Z}^{} \rightarrow \mathds{Z}^{*} \ni f(x) = 1 - x\) seems to fit the bill nicely. + +\begin{enumerate} +\item \(f\) is a bijection since we have an inverse \(x = 1 - f(x)\) +\item \(f(a \oplus b) = 1 - (a \oplus b) = 1 - (a + b - 1) = (1 - a) + (1 - b) = f(a) + f(b)\) and +\(f(a \odot b) = 1 - (a \odot b) = 1 - (a + b - ab) = (1-a) \cdot (1-b) = f(a) \cdot f(b)\) +\end{enumerate} + +\subsection{Question Twenty Four} +\label{sec:org07a0b7a} +\subsubsection{a} +\label{sec:org897ff21} +\begin{enumerate} +\item By the usual coordinate addition we know that \(a, b \in R \Rightarrow a + b \in R\) and is associative, commutative, and the additive identity is \((0, 0)\). +\item \(R\) is closed under multiplication: \(a, b \in R \Rightarrow a = (c, d) \wedge b = (e, f) \Rightarrow a \cdot b = (ce, de)\) and since \(c, d, e, f \in \mathds{R}\) then \((ce, de) \in \mathds{R} \times \mathds{R}\) by definition. +\item Multiplication is associative: \(a, b, c \in R \Rightarrow a = (d, e) \wedge b = (f, g) \wedge c = (h, i) \Rightarrow (a \cdot b) \cdot c = (df, ef) \cdot (h, i) = (dfh, efh)\) and \(a \cdot (b \cdot c) = (d, e) \cdot (fh, gh) = (dfh, efh)\) +\item Multiplication is distributive: \(a, b, c \in R \Rightarrow a = (d, e) \wedge b = (f, g) \wedge c = (h, i) \Rightarrow a(b + c) = (e, f) \cdot (f + h, g + i) = (ef + eh, ff + fh) = (ef, ff) + (eh, fh) = a \cdot b + a \cdot c\) +and \(a, b, c \in R \Rightarrow a = (d, e) \wedge b = (f, g) \wedge c = (h, i) \Rightarrow (a + b) \cdot c = (d + f, e + g) \cdot (h, i) = (dh + fh, eh + gh) = (dh, eh) + (fh, gh) = a \cdot c + b \cdot c\) +\end{enumerate} +\subsubsection{b} +\label{sec:org92e2744} +Consider the function \(f: R \rightarrow M(\mathds{R})\) is an isomorphism, such that \(f((a, b)) =\) \(\begin{smallmatrix} a & 0 \\ b & 0 \end{smallmatrix}\), then: +\begin{enumerate} +\item \(f\) is surjective since every element in the range has a domain element \(\begin{smallmatrix} a & 0 \\ b & 0 \end{smallmatrix} = y \ni f((a, b)) = y\) +\item \(f\) is injective since \(f((c, d) = x) = f((e, f) = y) \Rightarrow\) \(\begin{smallmatrix} c & 0 \\ d & 0 \end{smallmatrix}\) = \(\begin{smallmatrix} e & 0 \\ f & 0 \end{smallmatrix}\) \(\Rightarrow c = e \wedge d = f \Rightarrow x = y\) +\item \(f((c, d) = x) + f((e, f) = y) \Rightarrow\) \(\begin{smallmatrix} c & 0 \\ d & 0 \end{smallmatrix}\) + \(\begin{smallmatrix} e & 0 \\ f & 0 \end{smallmatrix}\) = \(\begin{smallmatrix} c + e & 0 \\ d + f & 0 \end{smallmatrix}\) +\(= f(x + y)\), and \(f((c, d) = x) \cdot f((e, f) = y) \Rightarrow\) \(\begin{smallmatrix} c & 0 \\ d & 0 \end{smallmatrix}\) \(\cdot\) \(\begin{smallmatrix} e & 0 \\ f & 0 \end{smallmatrix}\) = \(\begin{smallmatrix} ce & 0 \\ de & 0 \end{smallmatrix}\) +\(= f(x \cdot y)\) +\end{enumerate} +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/alg_structures_assn_6.org b/Homework/math4310/alg_structures_assn_6.org new file mode 100644 index 0000000..501130d --- /dev/null +++ b/Homework/math4310/alg_structures_assn_6.org @@ -0,0 +1,75 @@ +#+TITLE: Assignment Five +#+AUTHOR: Lizzy Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} +#+LATEX: \setlength\parindent{0pt} +#+OPTIONS: toc:nil + +* Section 4.1 +** Question One +*** d +$2x^5 + x^4 + 6x^2 + 3x + 2$ + +** Question Three +*** b +\begin{verbatim} +>>> list(filter(lambda x: x, \ + [f"{a}x^2 + {b}x + {c}" if not a == 0 or not b == 0 else "" \ + for a in range(3) for b in range(3) for c in range(3)])) +\end{verbatim} + +{'0x^2 + 1x + 0', + '0x^2 + 1x + 1', + '0x^2 + 1x + 2', + '0x^2 + 2x + 0', + '0x^2 + 2x + 1', + '0x^2 + 2x + 2', + '1x^2 + 0x + 0', + '1x^2 + 0x + 1', + '1x^2 + 0x + 2', + '1x^2 + 1x + 0', + '1x^2 + 1x + 1', + '1x^2 + 1x + 2', + '1x^2 + 2x + 0', + '1x^2 + 2x + 1', + '1x^2 + 2x + 2', + '2x^2 + 0x + 0', + '2x^2 + 0x + 1', + '2x^2 + 0x + 2', + '2x^2 + 1x + 0', + '2x^2 + 1x + 1', + '2x^2 + 1x + 2', + '2x^2 + 2x + 0', + '2x^2 + 2x + 1', + '2x^2 + 2x + 2'} + +** Question Five +Unfortunately, latex'ing long division is not trivial. Sorry in advance. + +#+attr_latex: :width 400px +[[./q5.jpeg]] + +** Question Six +*** c +No, since two polynomials of degree $\leq k$ with $k=2$, under multiplication, could produce +a polynomial of degree 4. +*** d ++ Closed under addition (two polynomials with even degrees can only add to polynomials with even degrees) ++ Closed under multiplication (two polynomials with even degrees can only multiply to polynomials with even degrees) ++ 0_R exists in the set ++ For a polynomial $a$ with only even powers, then $a + x = 0_R$ implies that $a = -x$ which will only change coefficients + +Seems like a subring (although not rigorously shown) to me! + +*** e +Not a subring, since $x^3 \cdot x = x^4$, with $x^3$ and $x$ both elements in the described set. +** Question Eleven + +\begin{verbatim} +>>> list(filter(lambda x: ((3 + x) % 9 == 0) and ((3 * x) % 9 == 0), range(9))) +[6] +\end{verbatim} + +$(1 + 3x)(1 + 6x) = 1 + 6x + 3x + 18x^2 = 1 + 9x + 18x^2 = 1$ + + diff --git a/Homework/math4310/alg_structures_assn_6.pdf b/Homework/math4310/alg_structures_assn_6.pdf Binary files differnew file mode 100644 index 0000000..dc9d43e --- /dev/null +++ b/Homework/math4310/alg_structures_assn_6.pdf diff --git a/Homework/math4310/alg_structures_assn_6.tex b/Homework/math4310/alg_structures_assn_6.tex new file mode 100644 index 0000000..3ca16ba --- /dev/null +++ b/Homework/math4310/alg_structures_assn_6.tex @@ -0,0 +1,111 @@ +% Created 2023-03-01 Wed 08:52 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} +\author{Lizzy Hunt} +\date{\today} +\title{Assignment Five} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Assignment Five}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Section 4.1} +\label{sec:orge1c762a} +\subsection{Question One} +\label{sec:org6594d20} +\subsubsection{d} +\label{sec:orgf9d77b6} +\(2x^5 + x^4 + 6x^2 + 3x + 2\) + +\subsection{Question Three} +\label{sec:org8e6afc5} +\subsubsection{b} +\label{sec:org7f9f78d} +\begin{verbatim} +>>> list(filter(lambda x: x, \ + [f"{a}x^2 + {b}x + {c}" if not a == 0 or not b == 0 else "" \ + for a in range(3) for b in range(3) for c in range(3)])) +\end{verbatim} + +\{'0x\textsuperscript{2} + 1x + 0', + '0x\textsuperscript{2} + 1x + 1', + '0x\textsuperscript{2} + 1x + 2', + '0x\textsuperscript{2} + 2x + 0', + '0x\textsuperscript{2} + 2x + 1', + '0x\textsuperscript{2} + 2x + 2', + '1x\textsuperscript{2} + 0x + 0', + '1x\textsuperscript{2} + 0x + 1', + '1x\textsuperscript{2} + 0x + 2', + '1x\textsuperscript{2} + 1x + 0', + '1x\textsuperscript{2} + 1x + 1', + '1x\textsuperscript{2} + 1x + 2', + '1x\textsuperscript{2} + 2x + 0', + '1x\textsuperscript{2} + 2x + 1', + '1x\textsuperscript{2} + 2x + 2', + '2x\textsuperscript{2} + 0x + 0', + '2x\textsuperscript{2} + 0x + 1', + '2x\textsuperscript{2} + 0x + 2', + '2x\textsuperscript{2} + 1x + 0', + '2x\textsuperscript{2} + 1x + 1', + '2x\textsuperscript{2} + 1x + 2', + '2x\textsuperscript{2} + 2x + 0', + '2x\textsuperscript{2} + 2x + 1', + '2x\textsuperscript{2} + 2x + 2'\} + +\subsection{Question Five} +\label{sec:orgf501bb3} +Unfortunately, latex'ing long division is not trivial. Sorry in advance. + +\begin{center} +\includegraphics[width=400px]{./q5.jpeg} +\end{center} + +\subsection{Question Six} +\label{sec:orgf9d6188} +\subsubsection{c} +\label{sec:org0feefbc} +No, since two polynomials of degree \(\leq k\) with \(k=2\), under multiplication, could produce +a polynomial of degree 4. +\subsubsection{d} +\label{sec:org18fd125} +\begin{itemize} +\item Closed under addition (two polynomials with even degrees can only add to polynomials with even degrees) +\item Closed under multiplication (two polynomials with even degrees can only multiply to polynomials with even degrees) +\item 0\textsubscript{R} exists in the set +\item For a polynomial \(a\) with only even powers, then \(a + x = 0_R\) implies that \(a = -x\) which will only change coefficients +\end{itemize} + +Seems like a subring (although not rigorously shown) to me! + +\subsubsection{e} +\label{sec:org6de4719} +Not a subring, since \(x^3 \cdot x = x^4\), with \(x^3\) and \(x\) both elements in the described set. +\subsection{Question Eleven} +\label{sec:orgb3179d8} + +\begin{verbatim} +>>> list(filter(lambda x: ((3 + x) % 9 == 0) and ((3 * x) % 9 == 0), range(9))) +[6] +\end{verbatim} + +\((1 + 3x)(1 + 6x) = 1 + 6x + 3x + 18x^2 = 1 + 9x + 18x^2 = 1\) +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/alg_structures_assn_7.org b/Homework/math4310/alg_structures_assn_7.org new file mode 100644 index 0000000..d683a34 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_7.org @@ -0,0 +1,175 @@ +#+TITLE: Assignment Seven +#+AUTHOR: Lizzy Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} +#+LATEX: \setlength\parindent{0pt} +#+OPTIONS: toc:nil + + +* Section 4.2 +** Question Five +*** b +\begin{align*} +x^5 + x^4 + 2x^3 - x^2 - x - 2 &= (x - 1)(x^4 + 2x^3 + 5x^2 + 4x + 4) + (-x^3 - x + 2) \\ +x^4 + 2x^3 + 5x^2 + 4x + 4 &= (-x-2)(-x^3 - x + 2) + (4x^2 + 4x + 8)\\ +-x^3 - x + 2 &= (\frac{-x}{4})(4x^2 + 4x + 8) + 0 +\end{align*} + +$(4x^2 + 4x + 8) = 4(x^2 + x + 2)$ + +$x^2 + x + 2$ +*** c +$deg(d) = 2$ is the greatest degree of a possible common divisor, so we'll stick with $x^2 - 1$. +*** g +\begin{align*} +2x^4 + 5x^3 - 5x - 2 &= (x + 4)(2x^3 - 3x^2 - 2x) + (14x^2 + 3x - 2) \\ +2x^3 - 3x^2 - 2x &= (\frac{x}{7} - \frac{12}{49})(14x^2 + 3x - 2) + (\frac{-48x - 24}{49}) \\ +14x^2 + 3x - 2 &= (\frac{-7x}{24})(\frac{-48x - 24}{49}) + 0 +\end{align*} + +$\frac{-48x - 24}{49} = \left(\frac{49}{-48}\right)\left(\frac{\left(-48x-24\right)}{49}\right) = x + \frac{1}{2}$ + +$x + \frac{1}{2}$ +** Question Ten +$x^3 - 3abx + a^3 + b^3$ can be factored to $(a + b + x) (a^2 - a b - a x + b^2 - b x + x^2)$, so $a + b + x$ is the gcd. + +* Section 4.3 +** Question Three +*** a +{ $x^2 + x + 1$, $2x^2 + 2x + 2$, $3x^2 + 3x + 3$, $4x^2 + 4x + 4$ } +*** b +{ $3x + 2$, $6x + 4$, $2x + 6$, $5x + 1$, $x + 3$, $4x + 5$ } + +** Question Six +Assume that $x^2 + 1$ is in fact reducible. Then, $x^2 + 1 = (ax + b)(cx + d)$. Thus, $ax \cdot cx = x^2 \Rightarrow ac = 1$, $axd + bcx = 0 \Rightarrow ad + bc = 0$, and $bd = 1$ with $a,b,c,d$ all being nonzero. + +Then, $a = \frac{1}{c}$ and $d = \frac{1}{b}$, so $ad = -bc \Rightarrow \frac{1}{cb} = - bc$, which is impossible. + +** Question Nine +*** a +$x^2 + x + 1$ + +*** b +$x^3 + x^2 + 1$ and $x^3 + x + 1$ + +** Question Ten +*** a +In $\mathds{Q}[x]$, no. In $\mathds{R}[x]$, yes: $x^2 - 3 = (x - \sqrt{3})(x + \sqrt{3})$. + +*** b +Yes, in both fields: $x^2 + x - 2 = (x + 2)(x - 1)$ + +** Question Eleven +Assume that $x^3 - 3$ were reducible in $\mathds{Z}_7 [x]$. Then, there must be a monic factor of degree one, as +$x^3 - 3 = g(x)h(x) \Rightarrow deg(x^3 - 3) = deg(g(x)h(x)) \Rightarrow 3 = deg(g(x)) + deg(h(x))$ by Theorem 4.2, and either $deg(g(x))$ or $deg(h(x))$ must be one, with the other, two. + +So, one of the factors must be of the form $x + a, a \in \mathds{Z}_7$. None such factor exists since polynomial division always returns a non-zero remainder: + +$x \nmid x^3 - 3$, trivially. + +$\frac{x^3 - 3}{x + 1}$ gives a remainder of $4$. + +$\frac{x^3 - 3}{x + 2}$ gives a remainder of $-11 \equiv_7 3$. + +$\frac{x^3 - 3}{x + 3}$ gives a remainder of $-30 \equiv_7 5$. + +$\frac{x^3 - 3}{x + 4}$ gives a remainder of $-67 \equiv_7 3$. + +$\frac{x^3 - 3}{x + 5}$ gives a remainder of $-128 \equiv_7 5$. + +$\frac{x^3 - 3}{x + 6}$ gives a remainder of $-219 \equiv_7 5$. + +** Question Twelve +In $\mathds{Q}[x]$, $x^4 - 4 = (x^2 - 2)(x^2 + 2)$ + +In $\mathds{R}[x]$, $x^4 - 4 = (x - \sqrt{2})(x + \sqrt{2})(x^2 + 2)$ + +In $\mathds{C}[x]$, $x^4 - 4 = (x - \sqrt{2})(x + \sqrt{2})(x - i \sqrt{2})(x + i \sqrt{2})$ + +** Question Fourteen +$x^2 + x \equiv_6 (x + 4)(x + 3)$ + +$x^2 + x \equiv_6 x(x + 1)$ + +* Section 4.4 +** Question Two +*** c +By Theorem 4.15, the remainder is $f(-1) = 5$ + +** Question Three +*** c +If the remainder of $\frac{f(x)}{h(x)}$ is 0, then $h$ is a factor of $f$, so using +Theorem 4.15 we can find that $f(-2) = -55 \equiv_5 0$, so $h$ is indeed a factor. + +** Question Four +*** b +We need to find k such that $f(-1) = 0 (mod 5)$ + +\begin{verbatim} +>>> f = lambda k,x: (x**4 + 2 * x**3 - 3 * x**2 + k * x + 1) % 5 +>>> for i in range(5): +... if f(i, -1) == 0: +... print(i) +... +2 +\end{verbatim} + +$k=2$ works nicely! + +** Question Seven +\begin{verbatim} +>>> set(filter(lambda x: (x**7 - x) % 7 == 0, range(7))) +{0, 1, 2, 3, 4, 5, 6} +\end{verbatim} + +Shows that each element is a root, so the factoring is correct by the Factor Theorem. + +** Question Eight +*** b +The polynomial is irreducible since its only roots are $\pm \sqrt{7} \notin \mathds{Q}$, by Corollary 4.19 + +*** d +\begin{verbatim} +>>> set(filter(lambda x: (2 * x**3 + x**2 + 2 * x + 2) % 5 == 0, range(5))) +set() +\end{verbatim} + +It's irreducible since there are no roots in $\mathds{Z}_5$. + +** Question Nine +\begin{verbatim} +>>> def find_irr_mon_polys(deg, mod): +... z_s = range(mod) +... polys = set() +... for b in z_s: +... for c z_s: +... f_repr = f"x^2 + {b}x + {c}" +... f = lambda x: (x**2 + b*x + c) % mod +... if not any(map(lambda x: f(x) == 0, z_s)): +... polys.add(f_repr) +... return polys + +>>> find_irr_mon_polys(2, 5) +\end{verbatim} + +{ $x^2 + 0x + 2, + x^2 + 0x + 3, + x^2 + 1x + 1, + x^2 + 1x + 2, + x^2 + 2x + 3, + x^2 + 2x + 4, + x^2 + 3x + 3, + x^2 + 3x + 4, + x^2 + 4x + 1, + x^2 + 4x + 2$ } + +\begin{verbatim} +>>> find_irr_mon_polys(2, 3) +\end{verbatim} +{ $x^2 + 0x + 1, x^2 + 1x + 2, x^2 + 2x + 2$ } + +** Question Thirteen +*** a +If $f(x) = cg(x)$ with $c \neq 0_F$, then $g(x) = c^{-1}f(x)$ and $f(x) = c^{-1}g(x)$. Then, $g(y) = 0_F \Leftrightarrow f(y) = 0_F$. +*** b +No, consider $f(x) = x$ and $g(x) = x^2$ in $\mathds{Z}$, then $f$ and $g$ share $0$ as their only root, but they are not associates. diff --git a/Homework/math4310/alg_structures_assn_7.pdf b/Homework/math4310/alg_structures_assn_7.pdf Binary files differnew file mode 100644 index 0000000..535c3c8 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_7.pdf diff --git a/Homework/math4310/alg_structures_assn_7.tex b/Homework/math4310/alg_structures_assn_7.tex new file mode 100644 index 0000000..d38f7d9 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_7.tex @@ -0,0 +1,234 @@ +% Created 2023-03-16 Thu 18:22 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} +\author{Lizzy Hunt} +\date{\today} +\title{Assignment Seven} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Assignment Seven}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + + +\section{Section 4.2} +\label{sec:org39ef51e} +\subsection{Question Five} +\label{sec:orgafa157f} +\subsubsection{b} +\label{sec:org072214f} +\begin{align*} +x^5 + x^4 + 2x^3 - x^2 - x - 2 &= (x - 1)(x^4 + 2x^3 + 5x^2 + 4x + 4) + (-x^3 - x + 2) \\ +x^4 + 2x^3 + 5x^2 + 4x + 4 &= (-x-2)(-x^3 - x + 2) + (4x^2 + 4x + 8)\\ +-x^3 - x + 2 &= (\frac{-x}{4})(4x^2 + 4x + 8) + 0 +\end{align*} + +\((4x^2 + 4x + 8) = 4(x^2 + x + 2)\) + +\(x^2 + x + 2\) +\subsubsection{c} +\label{sec:orgb01ae88} +\(deg(d) = 2\) is the greatest degree of a possible common divisor, so we'll stick with \(x^2 - 1\). +\subsubsection{g} +\label{sec:org4766198} +\begin{align*} +2x^4 + 5x^3 - 5x - 2 &= (x + 4)(2x^3 - 3x^2 - 2x) + (14x^2 + 3x - 2) \\ +2x^3 - 3x^2 - 2x &= (\frac{x}{7} - \frac{12}{49})(14x^2 + 3x - 2) + (\frac{-48x - 24}{49}) \\ +14x^2 + 3x - 2 &= (\frac{-7x}{24})(\frac{-48x - 24}{49}) + 0 +\end{align*} + +\(\frac{-48x - 24}{49} = \left(\frac{49}{-48}\right)\left(\frac{\left(-48x-24\right)}{49}\right) = x + \frac{1}{2}\) + +\(x + \frac{1}{2}\) +\subsection{Question Ten} +\label{sec:org6ab06e1} +\(x^3 - 3abx + a^3 + b^3\) can be factored to \((a + b + x) (a^2 - a b - a x + b^2 - b x + x^2)\), so \(a + b + x\) is the gcd. + +\section{Section 4.3} +\label{sec:org9759eff} +\subsection{Question Three} +\label{sec:orgf67495a} +\subsubsection{a} +\label{sec:org3a3c23d} +\{ \(x^2 + x + 1\), \(2x^2 + 2x + 2\), \(3x^2 + 3x + 3\), \(4x^2 + 4x + 4\) \} +\subsubsection{b} +\label{sec:org0eff32f} +\{ \(3x + 2\), \(6x + 4\), \(2x + 6\), \(5x + 1\), \(x + 3\), \(4x + 5\) \} + +\subsection{Question Six} +\label{sec:org58db881} +Assume that \(x^2 + 1\) is in fact reducible. Then, \(x^2 + 1 = (ax + b)(cx + d)\). Thus, \(ax \cdot cx = x^2 \Rightarrow ac = 1\), \(axd + bcx = 0 \Rightarrow ad + bc = 0\), and \(bd = 1\) with \(a,b,c,d\) all being nonzero. + +Then, \(a = \frac{1}{c}\) and \(d = \frac{1}{b}\), so \(ad = -bc \Rightarrow \frac{1}{cb} = - bc\), which is impossible. + +\subsection{Question Nine} +\label{sec:orge1fd195} +\subsubsection{a} +\label{sec:org33e3a63} +\(x^2 + x + 1\) + +\subsubsection{b} +\label{sec:orgf9e0897} +\(x^3 + x^2 + 1\) and \(x^3 + x + 1\) + +\subsection{Question Ten} +\label{sec:org4da4dbc} +\subsubsection{a} +\label{sec:orgc043f8c} +In \(\mathds{Q}[x]\), no. In \(\mathds{R}[x]\), yes: \(x^2 - 3 = (x - \sqrt{3})(x + \sqrt{3})\). + +\subsubsection{b} +\label{sec:org68f2a14} +Yes, in both fields: \(x^2 + x - 2 = (x + 2)(x - 1)\) + +\subsection{Question Eleven} +\label{sec:org957dc65} +Assume that \(x^3 - 3\) were reducible in \(\mathds{Z}_7 [x]\). Then, there must be a monic factor of degree one, as +\(x^3 - 3 = g(x)h(x) \Rightarrow deg(x^3 - 3) = deg(g(x)h(x)) \Rightarrow 3 = deg(g(x)) + deg(h(x))\) by Theorem 4.2, and either \(deg(g(x))\) or \(deg(h(x))\) must be one, with the other, two. + +So, one of the factors must be of the form \(x + a, a \in \mathds{Z}_7\). None such factor exists since polynomial division always returns a non-zero remainder: + +\(x \nmid x^3 - 3\), trivially. + +\(\frac{x^3 - 3}{x + 1}\) gives a remainder of \(4\). + +\(\frac{x^3 - 3}{x + 2}\) gives a remainder of \(-11 \equiv_7 3\). + +\(\frac{x^3 - 3}{x + 3}\) gives a remainder of \(-30 \equiv_7 5\). + +\(\frac{x^3 - 3}{x + 4}\) gives a remainder of \(-67 \equiv_7 3\). + +\(\frac{x^3 - 3}{x + 5}\) gives a remainder of \(-128 \equiv_7 5\). + +\(\frac{x^3 - 3}{x + 6}\) gives a remainder of \(-219 \equiv_7 5\). + +\subsection{Question Twelve} +\label{sec:orge9f1b7e} +In \(\mathds{Q}[x]\), \(x^4 - 4 = (x^2 - 2)(x^2 + 2)\) + +In \(\mathds{R}[x]\), \(x^4 - 4 = (x - \sqrt{2})(x + \sqrt{2})(x^2 + 2)\) + +In \(\mathds{C}[x]\), \(x^4 - 4 = (x - \sqrt{2})(x + \sqrt{2})(x - i \sqrt{2})(x + i \sqrt{2})\) + +\subsection{Question Fourteen} +\label{sec:orge490368} +\(x^2 + x \equiv_6 (x + 4)(x + 3)\) + +\(x^2 + x \equiv_6 x(x + 1)\) + +\section{Section 4.4} +\label{sec:orgced6b81} +\subsection{Question Two} +\label{sec:org80309c5} +\subsubsection{c} +\label{sec:org684714e} +By Theorem 4.15, the remainder is \(f(-1) = 5\) + +\subsection{Question Three} +\label{sec:org4950bb3} +\subsubsection{c} +\label{sec:org38b222f} +If the remainder of \(\frac{f(x)}{h(x)}\) is 0, then \(h\) is a factor of \(f\), so using +Theorem 4.15 we can find that \(f(-2) = -55 \equiv_5 0\), so \(h\) is indeed a factor. + +\subsection{Question Four} +\label{sec:org5aa1b14} +\subsubsection{b} +\label{sec:orge7c045e} +We need to find k such that \(f(-1) = 0 (mod 5)\) + +\begin{verbatim} +>>> f = lambda k,x: (x**4 + 2 * x**3 - 3 * x**2 + k * x + 1) % 5 +>>> for i in range(5): +... if f(i, -1) == 0: +... print(i) +... +2 +\end{verbatim} + +\(k=2\) works nicely! + +\subsection{Question Seven} +\label{sec:orgecff464} +\begin{verbatim} +>>> set(filter(lambda x: (x**7 - x) % 7 == 0, range(7))) +{0, 1, 2, 3, 4, 5, 6} +\end{verbatim} + +Shows that each element is a root, so the factoring is correct by the Factor Theorem. + +\subsection{Question Eight} +\label{sec:orge5e9620} +\subsubsection{b} +\label{sec:org65737b6} +The polynomial is irreducible since its only roots are \(\pm \sqrt{7} \notin \mathds{Q}\), by Corollary 4.19 + +\subsubsection{d} +\label{sec:orga790f86} +\begin{verbatim} +>>> set(filter(lambda x: (2 * x**3 + x**2 + 2 * x + 2) % 5 == 0, range(5))) +set() +\end{verbatim} + +It's irreducible since there are no roots in \(\mathds{Z}_5\). + +\subsection{Question Nine} +\label{sec:org2cf5693} +\begin{verbatim} +>>> def find_irr_mon_polys(deg, mod): +... z_s = range(mod) +... polys = set() +... for b in z_s: +... for c z_s: +... f_repr = f"x^2 + {b}x + {c}" +... f = lambda x: (x**2 + b*x + c) % mod +... if not any(map(lambda x: f(x) == 0, z_s)): +... polys.add(f_repr) +... return polys + +>>> find_irr_mon_polys(2, 5) +\end{verbatim} + +\{ \(x^2 + 0x + 2, + x^2 + 0x + 3, + x^2 + 1x + 1, + x^2 + 1x + 2, + x^2 + 2x + 3, + x^2 + 2x + 4, + x^2 + 3x + 3, + x^2 + 3x + 4, + x^2 + 4x + 1, + x^2 + 4x + 2\) \} + +\begin{verbatim} +>>> find_irr_mon_polys(2, 3) +\end{verbatim} +\{ \(x^2 + 0x + 1, x^2 + 1x + 2, x^2 + 2x + 2\) \} + +\subsection{Question Thirteen} +\label{sec:org4f87227} +\subsubsection{a} +\label{sec:org32ba550} +If \(f(x) = cg(x)\) with \(c \neq 0_F\), then \(g(x) = c^{-1}f(x)\) and \(f(x) = c^{-1}g(x)\). Then, \(g(y) = 0_F \Leftrightarrow f(y) = 0_F\). +\subsubsection{b} +\label{sec:org84283d0} +No, consider \(f(x) = x\) and \(g(x) = x^2\) in \(\mathds{Z}\), then \(f\) and \(g\) share \(0\) as their only root, but they are not associates. +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/alg_structures_assn_9.odt b/Homework/math4310/alg_structures_assn_9.odt Binary files differnew file mode 100644 index 0000000..b874bc3 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_9.odt diff --git a/Homework/math4310/alg_structures_assn_9.pdf b/Homework/math4310/alg_structures_assn_9.pdf Binary files differnew file mode 100644 index 0000000..88a2686 --- /dev/null +++ b/Homework/math4310/alg_structures_assn_9.pdf diff --git a/Homework/math4310/alg_structures_assn_9.tex b/Homework/math4310/alg_structures_assn_9.tex new file mode 100644 index 0000000..f118c8b --- /dev/null +++ b/Homework/math4310/alg_structures_assn_9.tex @@ -0,0 +1,213 @@ +% Created 2023-03-26 Sun 19:34 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,landscape]{geometry} \usepackage{polynom} +\author{Lizzy Hunt} +\date{\today} +\title{Assignment Nine} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Assignment Nine}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Section 5.1} +\label{sec:org93c6765} +\subsection{Question One} +\label{sec:org1b933f1} +\subsubsection{b} +\label{sec:org9c622bd} +Yes. In \(F\), \(f(x) - g(x) = -x^3 + x = x^3 + x\). + +\begin{equation*} +\polylongdiv[style=A]{x^3 + x}{x^2+1} +\end{equation*} + +\subsubsection{c} +\label{sec:org3b14848} +No. \(f(x) - g(x) = x^5 - 2x^4 + 4x^3 - 8x^2 + 3x - 2\) + +\begin{equation*} +\polylongdiv[style=A]{x^5 - 2x^4 + 4x^3 - 8x^2 + 3x - 2}{x^3 - x^2 + x - 1} +\end{equation*} + +\subsection{Question Three} +\label{sec:org4de1470} +\(|\)\{ \(0, 1, x, x + 1, x^2, x^2 + 1, x^2 + x, x^2 + x + 1\) \}\(|\) = 8 + +\subsection{Question Four} +\label{sec:org7437458} +For every \(a,b,c \in \mathds{Z}_3\) we can generate a polynomial \(ax^2 + bx + c\), by part two of Corollary 5.5. \(3^3 = 27\) + +\subsection{Question Six} +\label{sec:orgf9878df} +By Corollary 5.5, all the congruence classes in \(F[x]\) are \(c \ni c \in F\). + +\subsection{Question Eight} +\label{sec:org7f80a1c} +\begin{align*} +f(x)k(x) &\equiv_{p(x)} g(x)k(x) \\ +& \Rightarrow p(x) | f(x)k(x) - g(x)k(x) \\ +& \Rightarrow p(x) | (f(x) - g(x))(k(x)) +\end{align*} + +By Theorem 4.10, since \(p(x)\) is relatively prime to \(k(x)\), \(p(x) | f(x) - g(x) \Rightarrow f(x) \equiv_{p(x)} g(x)\) + +\subsection{Question Eleven - TODO} +\label{sec:orgbb6f81a} + + +\section{Section 5.2} +\label{sec:org105955c} +\subsection{Question One} +\label{sec:org2696380} +The congruence classes are those in Section 5.1, Question Three as above. + +\begin{center} +\begin{tabular}{lllllllll} ++ & [0] & [1] & [x] & [x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1]\\[0pt] +[0] & [0] & [1] & [x] & [x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1]\\[0pt] +[1] & [1] & [0] & [x+1] & [x] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2} + x]\\[0pt] +[x] & [x] & [x + 1] & [0] & [1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1]\\[0pt] +[x + 1] & [x + 1] & [x] & [1] & [0] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2}]\\[0pt] +[x\textsuperscript{2}] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1] & [0] & [1] & [x] & [x + 1]\\[0pt] +[x\textsuperscript{2} + 1] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2} + x] & [1] & [0] & [x + 1] & [x]\\[0pt] +[x\textsuperscript{2} + x] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x] & [x+1] & [0] & [1]\\[0pt] +[x\textsuperscript{2} + x + 1] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2}] & [x+1] & [x] & [1] & [0]\\[0pt] +\end{tabular} +\end{center} + +\begin{center} +\begin{tabular}{lllllllll} +\(\cdot\) & [0] & [1] & [x] & [x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1]\\[0pt] +[0] & [0] & [0] & [0] & [0] & [0] & [0] & [0] & [0]\\[0pt] +[1] & [0] & [1] & [x] & [x + 1] & [x\textsuperscript{2}] & [x\textsuperscript{2} + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2} + x + 1]\\[0pt] +[x] & [0] & [x] & [x\textsuperscript{2}] & [x\textsuperscript{2}+x] & [x+1] & [1] & [x\textsuperscript{2}+x+1] & [x\textsuperscript{2}+1]\\[0pt] +[x + 1] & [0] & [x + 1] & [x\textsuperscript{2} + x] & [x\textsuperscript{2}+1] & [x\textsuperscript{2}+x+1] & [x\textsuperscript{2}] & [1] & [x]\\[0pt] +[x\textsuperscript{2}] & [0] & [x\textsuperscript{2}] & [x+1] & [x\textsuperscript{2}+x+1] & [x\textsuperscript{2}+x] & [x] & [x\textsuperscript{2}+1] & [1]\\[0pt] +[x\textsuperscript{2} + 1] & [0] & [x\textsuperscript{2} + 1] & [1] & [x\textsuperscript{2}] & [x] & [x\textsuperscript{2}+x+1] & [x+1] & [x\textsuperscript{2}+x]\\[0pt] +[x\textsuperscript{2} + x] & [0] & [x\textsuperscript{2} + x] & [x\textsuperscript{2}+x+1] & [1] & [x\textsuperscript{2}+1] & [x+1] & [x] & [x+1]\\[0pt] +[x\textsuperscript{2} + x + 1] & [0] & [x\textsuperscript{2} + x + 1] & [x\textsuperscript{2}+1] & [x] & [1] & [x\textsuperscript{2}+x] & [x\textsuperscript{2}] & [x+1]\\[0pt] +\end{tabular} +\end{center} + +Yes, this is a field since by Theorem 5.7, it is a commutative ring with identity, and each +non-zero row in the multiplication table contains the multiplicative identity (each is a unit). + +\subsection{Question Two - TODO} +\label{sec:org55dc879} + +\subsection{Question Three - TODO} +\label{sec:orga648a70} + +\subsection{Question Six} +\label{sec:orgc033877} +By Corollary 5.5, each congruence class can be rewritten with \(a,b \in \mathds{Q}\): \([ax + b]\). + +Addition is defined as \([ax + b] + [cx + d] = [(a + c)x + bd]\). + +\((ax + b)(cx + d) = acx^2 + dax + bcx + bd = acx^2 + (da + bc)x + bd\) + +\begin{equation*} +\polylongdiv[style=A]{acx^2 + (da + bc)x + bd}{x^2 - 2} +\end{equation*} + +Multiplication is thusly defined as \([ax + b] \cdot [cx + d] = [(ad + bc)x + (2ac + bd)]\) + +\subsection{Question Nine} +\label{sec:org76f0944} +Given that \([a + bx]\) is a nonzero congruence class, either +\(a > 0\) or \(b > 0\). Then let \(c = \frac{-a}{a^2 + b^2}\) and \(d = \frac{b}{a^2 + b^2}\). + +\begin{equation*} +\polylongdiv[style=A]{acx^2 + (da + bc)x + bd}{x^2 + 1} +\end{equation*} + +\begin{align*} +[ax + b][cx + d] & = [(ad + bc)x + (bd - ac)] \\ +&= [(\frac{ab}{a^2 + b^2} + \frac{-ab}{a^2 + b^2})x + \frac{b^2}{a^2 + b^2} - \frac{-a^2}{a^2 + b^2}] \\ +&= [0x + \frac{b^2 + a^2}{a^2 + b^2}] \\ +&= [1] +\end{align*} + +\section{Section 5.3} +\label{sec:org82d2650} +\subsection{Question One} +\label{sec:org2711f62} +\subsubsection{a} +\label{sec:org805523d} +\(x^3 + 2x^2 + x + 1\) does not have any roots in \mathds{Z}\textsubscript{3}, so by Corollary 4.19 it must be irreducible, +and thus a field by 5.10 + +\subsubsection{b} +\label{sec:orgf91e167} +This is not a field by Theorem 5.10 since 2 is a root in \(Z_5\), so by Corollary 4.19 it must be reducible. + +\subsubsection{c} +\label{sec:orgaf8d3bb} +This is not a field by Theorem 5.10 since \(x^4 + x^2 + 1 = (x^2 - x + 1)(x^2 + x + 1) \equiv_2 (x^2 + x + 1)^2\) shows \(x^4 + x^2 + 1\) is reducible. + +\subsection{Question Two} +\label{sec:org09929ee} +\subsubsection{a} +\label{sec:org889a4d4} +Since \(\mathds{Q} (\sqrt{2})\) is a subset of \(\mathds{R}\), multiplication and addition are associative, commutative, and distributive. + +The additive identity of \$\mathds{Q} (\sqrt{2}) is \(0 + 0\sqrt{2}\) and the multiplicative identity is \(1 + 0\sqrt{2}\). + +It must be a field since every non-zero element \(a + b \sqrt{2}\) is a unit: + +\begin{align*} +(a + b\sqrt{2})x = 1 & \Rightarrow x = \frac{1}{a + b\sqrt{2}} \\ +& \Rightarrow x = \frac{a - b\sqrt{2}}{(a + b\sqrt{2})(a - b \sqrt{2})} \\ +& \Rightarrow x = \frac{a}{a^2 - 2b^2} - \frac{b}{a^2 - 2b^2}\sqrt{2} \\ +\end{align*} + +\subsubsection{b} +\label{sec:orgbfbb6ba} +Every element in \(\mathds{Q} / (x^2 - 2)\) can be rewritten as a member of the congruence class \([ax + b]\) with \(a, b \in \mathds{Q}\) by Corollary 5.5. + +Then, we can define a function \(f\) such that \(f([ax + b]) = a + b\sqrt{2}\) so that \(f(x) \in \mathds{Q}(\sqrt{2})\). + +\(f\) is thus an isomorphism since (a chance of redemption from my midterm \(\ddot\smile\)): + +\begin{itemize} +\item \(f\) is injective since \(f([ax + b]) = f([cx + d]) \Rightarrow a + b\sqrt{2} = c + d\sqrt{2} \Rightarrow a = c \wedge b = d\) +\item \(f\) is surjective since each \(a + b\sqrt{2}\) is uniquely mapped to \([ax + b]\) +\item \$f([ax + b] + [cx + d]) = f([(a + c)x + (b + d)]) = (a + c) + (b + d)\sqrt{2} = (a + b\sqrt{2}) + (c + d\sqrt{2}) = f([ax + b]) + f([cx + d]) +\end{itemize} + +\subsection{Question Five} +\label{sec:org246fde8} +\subsubsection{a} +\label{sec:org748a4c5} +Since \(\mathds{Q} (\sqrt{3})\) is a subset of \(\mathds{R}\), multiplication and addition are associative, commutative, and distributive. + +The additive identity of \$\mathds{Q} (\sqrt{3}) is \(0 + 0\sqrt{3}\) and the multiplicative identity is \(1 + 0\sqrt{3}\). + +It must be a field since every non-zero element \(r + s \sqrt{3}\) is a unit (by first assuming that the inverse of \(r + s\sqrt{3}\) from the +back of the book, \(\frac{r}{r^2 - 3s^2} s \frac{s}{r^2 - 3s^2}\sqrt{3}\): + +\begin{align*} +(a + b\sqrt{3})x = 1 & \Rightarrow x = \frac{1}{a + b\sqrt{2}} \\ +& \Rightarrow x = \frac{a - b\sqrt{2}}{(a + b\sqrt{2})(a - b \sqrt{2})} \\ +& \Rightarrow x = \frac{a}{a^2 - 2b^2} - \frac{b}{a^2 - 2b^2}\sqrt{2} \\ +\end{align*} +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/alg_structures_midterm_1.org b/Homework/math4310/alg_structures_midterm_1.org new file mode 100644 index 0000000..db6dc8e --- /dev/null +++ b/Homework/math4310/alg_structures_midterm_1.org @@ -0,0 +1,119 @@ +#+TITLE: Midterm One +#+AUTHOR: Lizzy Hunt +#+STARTUP: entitiespretty fold inlineimages +#+LATEX_HEADER: \notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} +#+LATEX: \setlength\parindent{0pt} +#+OPTIONS: toc:nil + +* Question One +\begin{verbatim} +In [1]: sols = lambda n: set(filter(lambda x: (x**2 + x) % n == 0, range(n))) + +In [2]: sols(5) +Out[2]: {0, 4} + +In [3]: sols(6) +Out[3]: {0, 2, 3, 5} +\end{verbatim} + +* Question Two +$p | a \Rightarrow np = a$ + +$p | a + bc \Rightarrow mp = a + bc \Rightarrow mp = np + bc \Rightarrow (m - n)p = bc$ which implies $p$ is a factor of $bc$ ($p | bc$), so by Theorem 1.5, $p | b$ or $p | c$. + +* Question Three +From the multiplication table we can see that $e$ is the identity element $1_R$, the zero +element $0_R$ is $z$. From the addition table we find that every element is its own +additive inverse. + +** a +The units in this ring are ${e, g}$, and the zero divisors are ${a, b, c, f}$. + +** b +$3bd = 3(bd) = 3z = b$ + +$2ac = 2(ac) = 2b = b + b = z$ + +$g^{-1}f^3 = (g)(fff) (gf)(ff) = (d)(f) = d$ + +Thus, $3bd - 2ac + g^{-1}f^3 = b - z + d = b + d = f$. + +* Question Four +To get a hunch, + +#+BEGIN_SRC python +In [1]: import numpy as np + +In [2]: def find_counter(matrix_generator, in_ring, search_space=range(-100, 100)): +...: for a1 in search_space: +...: n = matrix_generator(a1) +...: for a2 in search_space: +...: m = matrix_generator(a2) +...: dot = np.dot(n, m) +...: add = np.add(n, m) +...: +...: if not in_ring(dot): +...: return (n, m, dot, '*') +...: if not in_ring(add): +...: return (n, m, add, '+') +...: +...: return None +...: + +In [3]: find_counter(lambda a: [[0, a], [0, -a]], \ + lambda m: m[0][1] == -m[1][1] and m[0][0] == 0 \ + and m[1][0] == 0) + +In [4]: find_counter(lambda a: [[0, a], [a, 0]], \ + lambda m: m[0][1] == m[1][0] and m[1][1] == 0 \ + and m[0][0] == 0) +Out[4]: +([[0, -100], [-100, 0]], + [[0, -100], [-100, 0]], + array([[10000, 0], + [ 0, 10000]]), + '*') +#+END_SRC +** a +Using Theorem 3.2, this is a ring: + +1. S_1 is closed under addition: $x, y \in S_1 \Rightarrow x + y =$ $\begin{smallmatrix} 0 & a \\ 0 & -a \end{smallmatrix}$ $+$ $\begin{smallmatrix} 0 & b \\ 0 & -b \end{smallmatrix}$ $\Rightarrow$ $x + y = \begin{smallmatrix} 0 & a + b \\ 0 & (-a) + (-b) \end{smallmatrix} = \begin{smallmatrix} 0 & a + b \\ 0 & -(a + b) \end{smallmatrix}$ which satisfies the rule +2. S_1 is closed under multiplication: $x, y \in S_1 \Rightarrow x \cdot y =$ $\begin{smallmatrix} 0 & a \\ 0 & -a \end{smallmatrix}$ $\cdot$ $\begin{smallmatrix} 0 & b \\ 0 & -b \end{smallmatrix}$ $\Rightarrow$ $x \cdot y =$ $\begin{smallmatrix} 0 + (a)(0) & 0(b) + a(-b) \\ 0 + (-a)(0) & 0b + (-a)(-b) \end{smallmatrix}$ $=$ $\begin{smallmatrix} 0 & -ab \\ 0 & ab \end{smallmatrix}$ which satisfies the rule +3. $0_R_{} = 0_{S_1} =$ $\begin{smallmatrix} 0 & 0 \\ 0 & 0 \end{smallmatrix}$ +4. $a \in S_1 \Rightarrow a + x = 0_R \wedge x \in S_1$ since $\begin{smallmatrix} 0 & a \\ 0 & -a \end{smallmatrix}$ $+$ $x = 0_{S_1} =$ $\begin{smallmatrix} 0 & 0 \\ 0 & 0 \end{smallmatrix}$ $\Rightarrow x =$ $\begin{smallmatrix} 0 & -a \\ 0 & a \end{smallmatrix}$ $\in S_1$ + +** b +$\begin{smallmatrix} 0 & -100 \\ -100 & 0 \end{smallmatrix}$ $\cdot$ $\begin{smallmatrix} 0 & -100 \\ -100 & 0 \end{smallmatrix}$ = $\begin{smallmatrix} 10000 & 0 \\ 0 & 10000 \end{smallmatrix}$ is not in the ring. + +* Question Five +No, it is not a homomorphism from the definition in 3.3. + +Consider $n =$ $\begin{smallmatrix} 0 & 0 \\ 0 & 1 \end{smallmatrix}$ and $m =$ $\begin{smallmatrix} 1 & 0 \\ 0 & 0 \end{smallmatrix}$. + +Then $nm =$ $\begin{smallmatrix} 0 & 0 \\ 0 & 0 \end{smallmatrix}$ and thus $Trace(n) \cdot Trace(m) = 1 \wedge Trace(nm) = 0 \Rightarrow f(n)f(m) \neq f(nm)$. + +* Question Six +No, I don't believe $f$ to be an isomorphism. +** Lemma +We need to show that $x \in Q \wedge x \sqrt{2} = y \in Q \Rightarrow x = 0$. + +If $x \neq 0$ then $y$ can be represented as $\frac{a}{b}$ with $a, b \neq 0 \wedge a,b \in \mathds{Z}$ and $(a, b) = 1$. + +So, $x \sqrt{2} = \frac{a}{b} \Rightarrow x \sqrt{2} b = a \Rightarrow x^2(2b^2) = a^2$ and thus $2 | aa$, and by applying Corollary 1.6, $2 | a$. + +By substituting $2c = a$ (a is divisible by 2), $x^2(2b^2) = 4c^2 \Rightarrow x^2 b^2 = 2c^2$ which implies $2 | (x^2 b^2) \Rightarrow 2 | x$ or $2 | b$ (again by Corollary 1.6). + +But 2 cannot divide $b$ as well as $a$, since $(a, b) = 1$ and $b \neq 0$. + +Thus $2 | x$. So $x = 2d \Rightarrow 4d^2(2b^2) = a^2 \Rightarrow 4 | a^2$, so $4e = a$, and by similar logic for $b$ above, $4 | x$. +Then, subsituting $x = 4f \Rightarrow 16f^2(2b^2) = a^2 \Rightarrow 16 | a^2$. Again, $16 | x$. + +In fact, all range elements $R$ of the recursive function on the natural numbers $f \ni f(1) = 2, f(n) = f(n-1)^2 \text{\{} n > 1 \text{\}}$ must divide $x$. + +Thus, x must be sup($R$), or 0 (everything divides zero). Obviously, though, $R$ is unbounded on the right, so it follows $x = 0$. + +** Proof +$a, b \in Q(\sqrt{2}) \Rightarrow f(a) = n + m \sqrt{2} \wedge b = x + y \sqrt{2} \Rightarrow f(a) = n - m \sqrt{2} \vee f(b) = x - y \sqrt{2}$. + +$f$ is not injective; if we assume $f(a) = f(b) \Rightarrow a = b$ then $f(a) - f(b) = 0 \Rightarrow n - m \sqrt{2} - x - y \sqrt{2} = 0 \Rightarrow 0 = (n-x) - (m + y)\sqrt{2} \Rightarrow n-x = (m+y)\sqrt{2}$ and, as $n-x \in Q$ since +Q is a ring and by definition, $(m + y)\sqrt{2} \in Q$ implies $(m + y) = 0$ by the lemma, thus $m = -y$. But $a = b \Rightarrow m = y$, a contradiction. diff --git a/Homework/math4310/alg_structures_midterm_1.pdf b/Homework/math4310/alg_structures_midterm_1.pdf Binary files differnew file mode 100644 index 0000000..b57c5c6 --- /dev/null +++ b/Homework/math4310/alg_structures_midterm_1.pdf diff --git a/Homework/math4310/alg_structures_midterm_1.tex b/Homework/math4310/alg_structures_midterm_1.tex new file mode 100644 index 0000000..0babb7a --- /dev/null +++ b/Homework/math4310/alg_structures_midterm_1.tex @@ -0,0 +1,157 @@ +% Created 2023-02-21 Tue 22:21 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry} +\author{Lizzy Hunt} +\date{\today} +\title{Midterm One} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Midterm One}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Question One} +\label{sec:org0a6f4f9} +\begin{verbatim} +In [1]: sols = lambda n: set(filter(lambda x: (x**2 + x) % n == 0, range(n))) + +In [2]: sols(5) +Out[2]: {0, 4} + +In [3]: sols(6) +Out[3]: {0, 2, 3, 5} +\end{verbatim} + +\section{Question Two} +\label{sec:orgc3f2004} +\(p | a \Rightarrow np = a\) + +\(p | a + bc \Rightarrow mp = a + bc \Rightarrow mp = np + bc \Rightarrow (m - n)p = bc\) which implies \(p\) is a factor of \(bc\) (\(p | bc\)), so by Theorem 1.5, \(p | b\) or \(p | c\). + +\section{Question Three} +\label{sec:org1b549c3} +From the multiplication table we can see that \(e\) is the identity element \(1_R\), the zero +element \(0_R\) is \(z\). From the addition table we find that every element is its own +additive inverse. + +\subsection{a} +\label{sec:org692c3d2} +The units in this ring are \({e, g}\), and the zero divisors are \({a, b, c, f}\). + +\subsection{b} +\label{sec:orgace7d7f} +\(3bd = 3(bd) = 3z = b\) + +\(2ac = 2(ac) = 2b = b + b = z\) + +\(g^{-1}f^3 = (g)(fff) (gf)(ff) = (d)(f) = d\) + +Thus, \(3bd - 2ac + g^{-1}f^3 = b - z + d = b + d = f\). + +\section{Question Four} +\label{sec:org2300bc4} +To get a hunch, + +\begin{verbatim} +In [1]: import numpy as np + +In [2]: def find_counter(matrix_generator, in_ring, search_space=range(-100, 100)): +...: for a1 in search_space: +...: n = matrix_generator(a1) +...: for a2 in search_space: +...: m = matrix_generator(a2) +...: dot = np.dot(n, m) +...: add = np.add(n, m) +...: +...: if not in_ring(dot): +...: return (n, m, dot, '*') +...: if not in_ring(add): +...: return (n, m, add, '+') +...: +...: return None +...: + +In [3]: find_counter(lambda a: [[0, a], [0, -a]], \ + lambda m: m[0][1] == -m[1][1] and m[0][0] == 0 \ + and m[1][0] == 0) + +In [4]: find_counter(lambda a: [[0, a], [a, 0]], \ + lambda m: m[0][1] == m[1][0] and m[1][1] == 0 \ + and m[0][0] == 0) +Out[4]: +([[0, -100], [-100, 0]], + [[0, -100], [-100, 0]], + array([[10000, 0], + [ 0, 10000]]), + '*') +\end{verbatim} +\subsection{a} +\label{sec:orgd1aade2} +Using Theorem 3.2, this is a ring: + +\begin{enumerate} +\item S\textsubscript{1} is closed under addition: \(x, y \in S_1 \Rightarrow x + y =\) \(\begin{smallmatrix} 0 & a \\ 0 & -a \end{smallmatrix}\) \(+\) \(\begin{smallmatrix} 0 & b \\ 0 & -b \end{smallmatrix}\) \(\Rightarrow\) \(x + y = \begin{smallmatrix} 0 & a + b \\ 0 & (-a) + (-b) \end{smallmatrix} = \begin{smallmatrix} 0 & a + b \\ 0 & -(a + b) \end{smallmatrix}\) which satisfies the rule +\item S\textsubscript{1} is closed under multiplication: \(x, y \in S_1 \Rightarrow x \cdot y =\) \(\begin{smallmatrix} 0 & a \\ 0 & -a \end{smallmatrix}\) \(\cdot\) \(\begin{smallmatrix} 0 & b \\ 0 & -b \end{smallmatrix}\) \(\Rightarrow\) \(x \cdot y =\) \(\begin{smallmatrix} 0 + (a)(0) & 0(b) + a(-b) \\ 0 + (-a)(0) & 0b + (-a)(-b) \end{smallmatrix}\) \(=\) \(\begin{smallmatrix} 0 & -ab \\ 0 & ab \end{smallmatrix}\) which satisfies the rule +\item \(0_R_{} = 0_{S_1} =\) \(\begin{smallmatrix} 0 & 0 \\ 0 & 0 \end{smallmatrix}\) +\item \(a \in S_1 \Rightarrow a + x = 0_R \wedge x \in S_1\) since \(\begin{smallmatrix} 0 & a \\ 0 & -a \end{smallmatrix}\) \(+\) \(x = 0_{S_1} =\) \(\begin{smallmatrix} 0 & 0 \\ 0 & 0 \end{smallmatrix}\) \(\Rightarrow x =\) \(\begin{smallmatrix} 0 & -a \\ 0 & a \end{smallmatrix}\) \(\in S_1\) +\end{enumerate} + +\subsection{b} +\label{sec:org3c559c3} +\(\begin{smallmatrix} 0 & -100 \\ -100 & 0 \end{smallmatrix}\) \(\cdot\) \(\begin{smallmatrix} 0 & -100 \\ -100 & 0 \end{smallmatrix}\) = \(\begin{smallmatrix} 10000 & 0 \\ 0 & 10000 \end{smallmatrix}\) is not in the ring. + +\section{Question Five} +\label{sec:orgb488460} +No, it is not a homomorphism from the definition in 3.3. + +Consider \(n =\) \(\begin{smallmatrix} 0 & 0 \\ 0 & 1 \end{smallmatrix}\) and \(m =\) \(\begin{smallmatrix} 1 & 0 \\ 0 & 0 \end{smallmatrix}\). + +Then \(nm =\) \(\begin{smallmatrix} 0 & 0 \\ 0 & 0 \end{smallmatrix}\) and thus \(Trace(n) \cdot Trace(m) = 1 \wedge Trace(nm) = 0 \Rightarrow f(n)f(m) \neq f(nm)\). + +\section{Question Six} +\label{sec:orgba6a67f} +No, I don't believe \(f\) to be an isomorphism. +\subsection{Lemma} +\label{sec:org72bdcf0} +We need to show that \(x \in Q \wedge x \sqrt{2} = y \in Q \Rightarrow x = 0\). + +If \(x \neq 0\) then \(y\) can be represented as \(\frac{a}{b}\) with \(a, b \neq 0 \wedge a,b \in \mathds{Z}\) and \((a, b) = 1\). + +So, \(x \sqrt{2} = \frac{a}{b} \Rightarrow x \sqrt{2} b = a \Rightarrow x^2(2b^2) = a^2\) and thus \(2 | aa\), and by applying Corollary 1.6, \(2 | a\). + +By substituting \(2c = a\) (a is divisible by 2), \(x^2(2b^2) = 4c^2 \Rightarrow x^2 b^2 = 2c^2\) which implies \(2 | (x^2 b^2) \Rightarrow 2 | x\) or \(2 | b\) (again by Corollary 1.6). + +But 2 cannot divide \(b\) as well as \(a\), since \((a, b) = 1\) and \(b \neq 0\). + +Thus \(2 | x\). So \(x = 2d \Rightarrow 4d^2(2b^2) = a^2 \Rightarrow 4 | a^2\), so \(4e = a\), and by similar logic for \(b\) above, \(4 | x\). +Then, subsituting \(x = 4f \Rightarrow 16f^2(2b^2) = a^2 \Rightarrow 16 | a^2\). Again, \(16 | x\). + +In fact, all range elements \(R\) of the recursive function on the natural numbers \(f \ni f(1) = 2, f(n) = f(n-1)^2 \text{\{} n > 1 \text{\}}\) must divide \(x\). + +Thus, x must be sup(\(R\)), or 0 (everything divides zero). Obviously, though, \(R\) is unbounded on the right, so it follows \(x = 0\). + +\subsection{Proof} +\label{sec:org69eb679} +\(a, b \in Q(\sqrt{2}) \Rightarrow f(a) = n + m \sqrt{2} \wedge b = x + y \sqrt{2} \Rightarrow f(a) = n - m \sqrt{2} \vee f(b) = x - y \sqrt{2}\). + +\(f\) is not injective; if we assume \(f(a) = f(b) \Rightarrow a = b\) then \(f(a) - f(b) = 0 \Rightarrow n - m \sqrt{2} - x - y \sqrt{2} = 0 \Rightarrow 0 = (n-x) - (m + y)\sqrt{2} \Rightarrow n-x = (m+y)\sqrt{2}\) and, as \(n-x \in Q\) since +Q is a ring and by definition, \((m + y)\sqrt{2} \in Q\) implies \((m + y) = 0\) by the lemma, thus \(m = -y\). But \(a = b \Rightarrow m = y\), a contradiction. +\end{document}
\ No newline at end of file diff --git a/Homework/math4310/alg_structurs_1.org b/Homework/math4310/alg_structurs_1.org new file mode 100644 index 0000000..ae92f51 --- /dev/null +++ b/Homework/math4310/alg_structurs_1.org @@ -0,0 +1,188 @@ +#+TITLE: Assignment One +#+AUTHOR: Logan Hunt +#+STARTUP: entitiespretty fold inlineimages latexpreview +#+LATEX_HEADER: \noindent \notag \usepackage{ dsfont } + +* Section 1.1 +** Question 5 +By reforming the given expression to show $ca$ as a multiple of $q$ and some remainder: + +\begin{align} +a = bq + r \\ +ca = (cb)q + (c)r +\end{align} + +and that $0 \leq r < b \Rightarrow 0 \leq cr < cb$, Theorem 1.1 tells us that there is only one unique quotient: +which is $q$, and the remainder is $(c)r$. + +** Question 7 +By Theorem 1.1, $a = bq + r, 0 \leq r \lt b$ implies that when b = 3, $a = 3q + r$ where $0 \leq r \lt b$, +thus $a \in \mathds{Z} \Rightarrow a = 3q + r$ where $r \in {0,1,2}$. + +By squaring $a$, we have three options which simplify to the form $3k$ or $3k + 1$: +1. $a^2 = (3q)^2 = 9q^2$ which is $3k \ni k = 3q^2$ +2. $a^2 = (3q + 1)^2 = 9q^2 + 3q + 1 = 3(3q^2 + q) + 1$ which is $3k + 1 \ni k = (3q^2 + q)$ +3. $a^2 = (3q + 2)^2 = 9q^2 + 6q + 4 = 3(3q^2 + 2q) + 4$ which is + $3l + 4 \ni l = (3q^2 + 2q)$ which is also $3l + 1 + 3 = 3(l+1) + 1$, + which again is $3k + 1 \ni k = l+1$ + +** Question 8 +By Theorem 1.1, $a = bq + r, 0 \leq r \lt b$ implies that when b = 4, $a = 4q + r$ where $0 \leq r \lt b$, +and thus $a = 4q + r$ and $r \in {0,1,2,3}$. + +Therefore we have four cases: + +1. $a = 4q$, and $a$ must be even which is invalid +2. $a = 4q + 1$, and $4q + 1 = 2k + 1 \ni k = 2q$ which fits the definition of an odd number +3. $a = 4q + 2$, thus $a$ must be even as $a = 2k \ni k = 2q + 1$ +4. $a = 4q + 3$, can be rewritten to $4q + 1 + 2$, which is odd: $2k + 1 \ni k = 2q + 1$ + +And thus any odd number can be rewritten as $4q + 1$ or $4q + 3$. + +** Question 10 +The division of $a$ and $c$ by $n$ can each be represented by + +\begin{align} +a = q_{a}n + r_a \\ +c = q_c_{}n + r_c +\end{align} + +where $0 \le r_a < n$ and $0 \le r_c < n$ by Theorem 1.1, and we can subtract each side of the +second equation from the first: + +\begin{align} +a - c = (q_{a}n + r_a) - (q_c_{}n + r_c) +\end{align} + +With this work now in hand, we will prove by showing that the conjecture is true both ways: + +For the first, we will suppose that $r_a = r_c$. Then, we find that +\begin{align} +a - c = n(q_a - q_c) \\ +a - c = nk +\end{align} +for some integer $k$. + +For the second, we will prove that if $a - c = nk$, when $a$ and $c$ are divided by $n$, +they leave the same remainder $r$. + +From the work we did previously, and by substituting $a-c = nk$, we find that +\begin{align} +a - c = (q_{a}n + r_a) - (q_c_{}n + r_c) \\ +nk = (q_{a}n + r_a) - (q_{c}n + r_c) \\ +nk = n(q_a - q_c) + (r_a - r_c) \\ +n(k - q_a + q_c) = r_a - r_c +\end{align} +and thus $r_a - r_c$ is a multiple of $n$. + +From the inequalities produced previously by Theorem 1.1, if $r_a \geq r_c$ then $0 \le r_a - r_c < n$ +and $-n < r_c - r_a \leq 0$. Else if $r_c \geq r_a$ then $0 \leq r_c - r_a < n$ and $-n < r_a - r_c \leq 0$. + +By combining the two cases, it must be that $ -n < r_a - r_c < n $, and from the above fact that +$r_a - r_c$ is a multiple of n, the only multiple of n in $(-n, n)$ is 0. Thus $r_a = r_c$. + +* Section 1.2 +** Question 1 +*** c +1, 57 and 112 are co-prime +** Question 3 +\begin{align} +a | b \Rightarrow \exists n \in \mathds{Z} \ni an = b \\ +b | c \Rightarrow \exists m \in \mathds{Z} \ni bm = c \\ +(an)m = c \Rightarrow a | c +\end{align} +** Question 4 +*** a +\begin{align} +a | b \Rightarrow \exists n \in \mathds{Z} \ni an = b \\ +a | c \Rightarrow \exists m \in \mathds{Z} \ni am = c \\ +a | (b + c) \Rightarrow \exists l \in \mathds{Z} \ni al = b + c \\ +al = an + am \\ +b + c = a(n + m) +\Rightarrow a | b+c +\end{align} +*** b +By continuing from "a": + +\begin{align} +br + ct = (an)r + (am)t \\ +\Rightarrow br + ct = a(nr + mt) \\ +\Rightarrow a | (br + ct) +\end{align} + + +** Question 7 +$|a|$ since $|a| \textbar a$ and $|a| \textbar 0$, and there cannot be an integer larger than +$|a|$ that divides $a$. + +** Question 9 +No, not every multiple of two factors of an integer divides that integer. + +For example, $3 | 9$ and $9 | 9$ but $27 \nmid 9$. + +** Question 15 +*** c +\begin{align} +1003 = (2)(456) + 91 \\ +456 = (5)(91) + 1 \\ +91 = (91)(1) + 0 \\ +\Rightarrow (1003, 456) = 1 +\end{align} +*** d +\begin{align} +322 = (2)(148) + 26 \\ +148 = (5)(26) + 18 \\ +26 = (1)(18) + 8 \\ +18 = (2)(8) + 2 \\ +8 = (4)(2) + 0 \\ +\Rightarrow (322, 148) = 2 +\end{align} + +** Question 17 + +\begin{align} +a | c \Rightarrow \exists n \in \mathds{Z} \ni an = c \\ +b | c \Rightarrow b | an +\end{align} + +And by Theorem 1.4, $(a, b) = 1 \Rightarrow b | n \Rightarrow ab | an \Rightarrow ab | c$: + +** Question 19 +Given some $d$ such that $d | a$ and $d | b$, then $a = nd$ and $b = md$. +\begin{align} +a | (b + c) \Rightarrow \exists p \in \mathds{Z} \ni ap = b + c \\ +c = ap - md \Rightarrow c = (nd)p - md \Rightarrow c = d(np - md) \Rightarrow d | c +\end{align} + +Since we're given that $(b, c) = 1 \Rightarrow (md, c) = 1$ and from the above fact that $d | c$, we can conclude +that $md = 1$. Therefore $(a, b) = (a, md) = (a, 1) = 1$. + +Given some $e$ such that $e | a$ and $e | c$, then $a = ue$ and $c = we$. +\begin{align} +a | (b + c) \Rightarrow \exists o \in \mathds{Z} \ni ao = b + c \\ +b = ao - we \Rightarrow b = (ue)o - we \Rightarrow b = e(uo - w) \Rightarrow e | b +\end{align} + +And from similar reasoning we can conclude that $(a, c) = (a, we) = (a, 1) = 1$. + +** Question 31 +*** a +$[6, 10] = 60$ + +$[4, 5, 6, 10] = 60$ + +$[20, 42] = 840$ + +$[2, 3, 14, 36, 42] = 252$ + +*** b +Let $m = [a_1, a_2, \ldots, a_k]$, then by the Division Algorithm, $t = mq + r$ for integers $q$ and $r$, +with $0 \leq r < m$. + +As given that all $a_i | t$ \Rightarrow $a_i | mq + r$, and as $mq$ is a multiple of the LCM including +a_i, $a_i$ must divide $mq$, and thus $a_i | r$. + +Because $a_i | r$, $r = na_i$ and is thus a multiple of all $a_i$, but the above statement that +$0 \leq r < m$ shows that $m$ - the LCM by definition - is greater than $r$. Therefore, $r = 0$ and +$t = mq \Rightarrow m | t$. + diff --git a/Homework/math4310/final.org b/Homework/math4310/final.org new file mode 100644 index 0000000..2189562 --- /dev/null +++ b/Homework/math4310/final.org @@ -0,0 +1,31 @@ +#+TITLE: Sample Problems + +WELL-DEFINED: +when x \in domain = y \in domain then f(x) = f(y) and each x \in domain has y \in range + +PRINCIPAL IDEAL: +ideal generated by an element + +SURJECTION: +every y \in range has (non-unique) x such that f(x) = y + +* Question Three +** a +$f$ is well defined as $f([a]_12)$ = $f([b]_12)$ implies $[a] = [b]$, as $[a]_4 = [b]_4$ implies that $a \equiv_4 b$ so $a - b \equiv_4 0 \Rightarrow a - b \equiv_4 12$ +which implies $a - b = 12n$ +** b +$f$ is a homomorphism: +f(a + b) = f(a) + f(b) by f([a]_12 + [b]_12) = f([a + b]_12) = [a + b]_4 = [a]_4 + [b]_4 = f([a]_12) + f([b]_12) +f(ab) = f(a)f(b) by f([a]_12 [b]_12) = f([ab]_12) = [ab]_4 = [a]_4[b]_4 = f([a]_12)f([b]_12) + +$f$ is surjective: +every element in the 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b/Homework/math4310/midterm_1.pdf diff --git a/Homework/math4310/midterm_1.tex b/Homework/math4310/midterm_1.tex new file mode 100644 index 0000000..e1a4a53 --- /dev/null +++ b/Homework/math4310/midterm_1.tex @@ -0,0 +1,151 @@ +% Created 2023-02-20 Mon 22:30 +% Intended LaTeX compiler: pdflatex +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage[T1]{fontenc} +\usepackage{graphicx} +\usepackage{longtable} +\usepackage{wrapfig} +\usepackage{rotating} +\usepackage[normalem]{ulem} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{capt-of} +\usepackage{hyperref} +\notindent \notag \usepackage{ dsfont } \usepackage{amsmath} \usepackage[a4paper,margin=1in,landscape]{geometry} +\author{Lizzy Hunt} +\date{\today} +\title{Midterm One} +\hypersetup{ + pdfauthor={Lizzy Hunt}, + pdftitle={Midterm One}, + pdfkeywords={}, + pdfsubject={}, + pdfcreator={Emacs 28.2 (Org mode 9.6.1)}, + pdflang={English}} +\begin{document} + +\maketitle +\setlength\parindent{0pt} + +\section{Question One} +\label{sec:org6315799} +\begin{verbatim} +In [1]: sols = lambda n: set(filter(lambda x: (x**2 + x) % n == 0, range(n))) + +In [2]: sols(5) +Out[2]: {0, 4} + +In [3]: sols(6) +Out[3]: {0, 2, 3, 5} +\end{verbatim} + +\section{Question Two - TODO} +\label{sec:org6c24b4c} + + +\section{Question Three} +\label{sec:org76bcd7b} +From the multiplication table we can see that \(e\) is the identity element \(1_R\), the zero +element \(0_R\) is \(z\). From the addition table we find that every element is its own +additive inverse. + +\subsection{a} +\label{sec:org983fdae} +The units in this ring are \({e, g}\), and the zero divisors are \({a, b, c, f}\). + +\subsection{b} +\label{sec:org9072029} +\(3bd = 3(bd) = 3z = b\) + +\(2ac = 2(ac) = 2b = b + b = z\) + +\(g^{-1}f^3 = (g)(fff) (gf)(ff) = (d)(f) = d\) + +Thus, \(3bd - 2ac + g^{-1}f^3 = b - z + d = b + d = f\). + +\section{Question Four} +\label{sec:orge571a7e} +To get a hunch, + +\begin{verbatim} +In [1]: import numpy as np + +In [2]: def find_counter(matrix_generator, in_ring, search_space=range(-100, 100)): + ...: for a1 in search_space: + ...: n = matrix_generator(a1) + ...: for a2 in search_space: + ...: m = matrix_generator(a2) + ...: dot = np.dot(n, m) + ...: add = np.add(n, m) + ...: + ...: if not in_ring(dot): + ...: return (n, m, dot, '*') + ...: if not in_ring(add): + ...: return (n, m, add, '+') + ...: + ...: return None + ...: + +In [3]: find_counter(lambda a: [[0, a], [0, -a]], lambda m: m[0][1] == -m[1][1] and m[0][0] == 0 and m[1][0] == 0) + +In [4]: In [31]: find_counter(lambda a: [[0, a], [a, 0]], lambda m: m[0][1] == m[1][0] and m[1][1] == 0 and m[0][0] == 0) +Out[4]: +([[0, -100], [-100, 0]], + [[0, -100], [-100, 0]], + array([[10000, 0], + [ 0, 10000]]), + '*') +\end{verbatim} +\subsection{a} +\label{sec:orge0ecef4} +Using Theorem 3.2, this is a ring: + +\begin{enumerate} +\item S\textsubscript{1} is closed under addition: \(x, y \in S_1 \Rightarrow x + y =\) \(\begin{smallmatrix} 0 & a \\ 0 & -a \end{smallmatrix}\) \(+\) \(\begin{smallmatrix} 0 & b \\ 0 & -b \end{smallmatrix}\) \(\Rightarrow\) \(x + y = \begin{smallmatrix} 0 & a + b \\ 0 & (-a) + (-b) \end{smallmatrix} = \begin{smallmatrix} 0 & a + b \\ 0 & -(a + b) \end{smallmatrix}\) which satisfies the rule +\item S\textsubscript{1} is closed under multiplication: \(x, y \in S_1 \Rightarrow x \cdot y =\) \(\begin{smallmatrix} 0 & a \\ 0 & -a \end{smallmatrix}\) \(\cdot\) \(\begin{smallmatrix} 0 & b \\ 0 & -b \end{smallmatrix}\) \(\Rightarrow\) \(x \cdot y =\) \(\begin{smallmatrix} 0 + (a)(0) & 0(b) + a(-b) \\ 0 + (-a)(0) & 0b + (-a)(-b) \end{smallmatrix}\) \(=\) \(\begin{smallmatrix} 0 & -ab \\ 0 & ab \end{smallmatrix}\) which satisfies the rule +\item \(0_R_{} = 0_{S_1} =\) \(\begin{smallmatrix} 0 & 0 \\ 0 & 0 \end{smallmatrix}\) +\item \(a \in S_1 \Rightarrow a + x = 0_R \wedge x \in S_1\) since \(\begin{smallmatrix} 0 & a \\ 0 & -a \end{smallmatrix}\) \(+\) \(x = 0_{S_1} =\) \(\begin{smallmatrix} 0 & 0 \\ 0 & 0 \end{smallmatrix}\) \(\Rightarrow x =\) \(\begin{smallmatrix} 0 & -a \\ 0 & a \end{smallmatrix}\) \(\in S_1\) +\end{enumerate} + +\subsection{b} +\label{sec:org1a8af9b} +\(\begin{smallmatrix} 0 & -100 \\ -100 & 0 \end{smallmatrix}\) \(\cdot\) \(\begin{smallmatrix} 0 & -100 \\ -100 & 0 \end{smallmatrix}\) = \(\begin{smallmatrix} 10000 & 0 \\ 0 & 10000 \end{smallmatrix}\) is not in the ring. + +\section{Question Five} +\label{sec:org85339f8} +No, it is not a homomorphism from the definition in 3.3. + +Consider \(n =\) \(\begin{smallmatrix} 0 & 0 \\ 0 & 1 \end{smallmatrix}\) and \(m =\) \(\begin{smallmatrix} 1 & 0 \\ 0 & 0 \end{smallmatrix}\). + +Then \(nm =\) \(\begin{smallmatrix} 0 & 0 \\ 0 & 0 \end{smallmatrix}\) and thus \(Trace(n) \cdot Trace(m) = 1 \wedge Trace(nm) = 0 \Rightarrow f(n)f(m) \neq f(nm)\). + +\section{Question Six} +\label{sec:org405929b} +No, I don't believe \(f\) to be an isomorphism. +\subsection{Lemma} +\label{sec:org323f970} +We need to show that \(x \in Q \wedge x \sqrt{2} = y \in Q \Rightarrow x = 0\). + +If \(x \neq 0\) then \(y\) can be represented as \(\frac{a}{b}\) with \(a, b \neq 0 \wedge a,b \in \mathds{Z}\) and \((a, b) = 1\). + +So, \(x \sqrt{2} = \frac{a}{b} \Rightarrow x \sqrt{2} b = a \Rightarrow x^2(2b^2) = a^2\) and thus \(2 | aa\), and by applying Corollary 1.6, \(2 | a\). + +By substituting \(2c = a\) (a is divisible by 2), \(x^2(2b^2) = 4c^2 \Rightarrow x^2 b^2 = 2c^2\) which implies \(2 | (x^2 b^2) \Rightarrow 2 | x\) or \(2 | b\) (again by Corollary 1.6). + +But 2 cannot divide \(b\) as well as \(a\), since \((a, b) = 1\) and \(b \neq 0\). + +Thus \(2 | x\). So \(x = 2d \Rightarrow 4d^2(2b^2) = a^2 \Rightarrow 4 | a^2\), so \(4e = a\), and by similar logic for \(b\) above, \(4 | x\). +Then, subsituting \(x = 4f \Rightarrow 16f^2(2b^2) = a^2 \Rightarrow 16 | a^2\). Again, \(16 | x\). + +In fact, all range elements \(R\) of the function on the natural numbers \$f \(\ni\) \$ \(f(1) = 2, f(n) = f(n-1)^2 { n > 1 }\) must divide \(x\). + +Thus, x must be sup(\(R\)) or 0. Obviously \(R\) is unbounded on the right, so it follows \(x = 0\). + +\subsection{Proof} +\label{sec:orge723534} +\(a, b \in Q(\sqrt{2}) \Rightarrow f(a) = n + m \sqrt{2} \wedge b = x + y \sqrt{2} \Rightarrow f(a) = n - m \sqrt{2} \vee f(b) = x - y \sqrt{2}\). + +\(f\) is not injective; if we assume \(f(a) = f(b) \Rightarrow a = b\) then \(f(a) - f(b) = 0 \Rightarrow n - m \sqrt{2} - x - y \sqrt{2} = 0 \Rightarrow 0 = (n-x) - (m + y)\sqrt{2} \Rightarrow n-x = (m+y)\sqrt{2}\) and, as \(n-x \in Q\) since +Q is a ring and by definition, \((m + y)\sqrt{2} \in Q\) implies \((m + y) = 0\) by the lemma, thus \(m = -y\). But for \(a = b\), \(m = y\), a contradiction. +\end{document}
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