diff --git a/assignments/main_text.pdf b/assignments/main_text.pdf index 85fd2e9..ea9d433 100644 Binary files a/assignments/main_text.pdf and b/assignments/main_text.pdf differ diff --git a/assignments/main_text.tex b/assignments/main_text.tex index ed27307..3c3eea0 100644 --- a/assignments/main_text.tex +++ b/assignments/main_text.tex @@ -1,6 +1,5 @@ \documentclass{template/homework} -\setcounter{secnumdepth}{0} % Makes sections unnumbered \usepackage{enumitem} % Gives access to better enumeration items \usepackage{tcolorbox} % Gives boxes \usepackage{subfiles} % Makes subfiles easier (and you want those) diff --git a/assignments/week1/main.pdf b/assignments/week1/main.pdf index a8cb92f..e5b5c1e 100644 Binary files a/assignments/week1/main.pdf and b/assignments/week1/main.pdf differ diff --git a/assignments/week1/main.tex b/assignments/week1/main.tex index 6ddbbd3..c763099 100644 --- a/assignments/week1/main.tex +++ b/assignments/week1/main.tex @@ -1,7 +1,8 @@ \documentclass[../main_text.tex]{subfiles} \begin{document} +\setcounter{exercise}{0} -\section{Assignment 1} +\part{Assignment 1} \exercise*[0.3.6] % For some reason I can't put a fitted tcbox here and I really don't like it @@ -132,7 +133,7 @@ So each set $A_i := \{i\} \forall i \in \N$. Since $\N$ is countably infinite, Each set is definitely finite, because they all contain just one element. Finally, the union of the collection of sets is equal to $\N$, which is not a finite set. -\exercise[6] +\exercise* \begin{tcolorbox} \begin{enumerate}[label=\emph{\alph*)}, wide] \item Compute $f(4/15)$. Find $q$ such that $f(q) = 108$. diff --git a/assignments/week2/main.pdf b/assignments/week2/main.pdf index 0ddca3f..5d46ff4 100644 Binary files a/assignments/week2/main.pdf and b/assignments/week2/main.pdf differ diff --git a/assignments/week2/main.tex b/assignments/week2/main.tex index ad580a0..d5480de 100644 --- a/assignments/week2/main.tex +++ b/assignments/week2/main.tex @@ -1,7 +1,8 @@ \documentclass[../main_text.tex]{subfiles} \begin{document} +\setcounter{exercise}{0} -\section{Assignment 2} +\part{Assignment 2} \exercise*[1.1.1] \begin{tcolorbox} @@ -17,7 +18,7 @@ Working out the right side with the distributive law, gives $0 < (-x*z)-(-x*y)$. Using $-1*-1 = 1$, gives $0 < (-xz)-(-xy)$, thus $0 < xy - xz$. The right part can be split again: $xz < xy$. Then, the < can be flipped, which gives $xy > xz$. \qed -\exercise[1.1.2] +\exercise*[1.1.2] \begin{tcolorbox} Let $S$ be an ordered set. Let $A \subset S$ be a non-empty finite subset. Then A is bounded. Furthermore, $\text{inf} A$ exists and in in $A$ and $\sup A$ exists and is in $A$. @@ -45,7 +46,7 @@ of $A$ in $A$ \footnote{It might even be that I have already proven that $A$ has Then that's also good enough to show that $A$ is bounded, since in order for $A$ to have a supremum, it must also be bounded.}. This will be left to the reader. -\exercise[1.1.5] +\exercise*[1.1.5] \begin{tcolorbox} Let $S$ be an ordered set. Let $A \subset S$ and suppose $b$ is an upper bound for $A$. Suppose $b \in A$. Show that $b = \sup A$. @@ -63,7 +64,7 @@ not an upper bound of $A$ and thus also not its supremum. If $c > b$, then $b$ i $c$ and therefore $c$ cannot be the supremum. The only option left is that $c=b$, and therefore $b = \sup A$. \qed -\exercise[1.1.6] +\exercise*[1.1.6] \begin{tcolorbox} Let $S$ be an ordered set. Let $A \subset S$ be nonempty and bounded above. Suppose $\sup A$ exists and $\sup A \notin A$. Show that $A$ contains a countably infinite subset. @@ -79,7 +80,7 @@ $a < b$ and $x < a $ $\forall x \in A$. So $b$ is in fact not the least upper bo which is in contradiction with our assumption earlier. Ergo, $|X| \geq |\N|$. Since $X$ then is at least of the same cardinality as $\N$, it must also contain a countably infinite subset. \qed -\exercise[1.2.7] +\exercise*[1.2.7] \begin{tcolorbox} Prove the arithmetic-geometric mean inequality. That is, for two positive real numbers $x, y$, we have \begin{equation*} @@ -103,7 +104,7 @@ Now to prove the second statement. We assume $x = y$ is a positive real number. \sqrt{xy}=\sqrt{x^2}=x=\frac{2x}{2}=\frac{x + y}{2}. \qed \end{equation*} -\exercise[1.2.9] +\exercise*[1.2.9] \begin{tcolorbox} Let $A$ and $B$ be two nonempty bounded sets of real numbers. Define the set $C := \{a + b : a \in A, b \in B\}$. Show that $C$ is a bounded set and that @@ -133,7 +134,7 @@ $y$ can be given by the supremum; $x \leq \sup A$ and $y \leq \sup B$. So, $\sup A similar argument can be given for the infimum, which is left to the reader. -\exercise[7] +\exercise* \begin{tcolorbox} Let \begin{equation*} diff --git a/assignments/week3/main.pdf b/assignments/week3/main.pdf index c7c94b5..ec7e2a0 100644 Binary files a/assignments/week3/main.pdf and b/assignments/week3/main.pdf differ diff --git a/assignments/week3/main.tex b/assignments/week3/main.tex index fa368ff..f196ad8 100644 --- a/assignments/week3/main.tex +++ b/assignments/week3/main.tex @@ -1,8 +1,34 @@ \documentclass[../main_text.tex]{subfiles} \begin{document} +\setcounter{exercise}{0} -\section{Assignment 3} +\part{Assignment 3} \exercise* +\begin{tcolorbox} + Suppose $x,y \in \R$ and $x < y$. Prove that there exists $i \in \R\backslash\Q$ such that $x < i < y$. +\end{tcolorbox} + +If either $x$ or $y$ (or both) are not rational numbers, we can simply take the average like so: $\frac{x+y}{2}$, +in a similar way we did for the rationals. Since $x$ or $y$ isn't rational, the resulting fraction will also not be +a rational and this proves the statement. + +Now if $x,y \in \Q$, we cannot use this average trick, because the resulting fraction will be a rational itself and +so it doesn't satisfy the restriction that it must be in $\R\backslash\Q$. So we have to take a different approach. + +Let $x,y \in \Q$ with $x < y$ and $m := \frac{x+y}{2}$, so $x < m < y$. Then, let $X = \{a \in \R : x < a < m\}$ and +let $Y = \{b \in \R : m < b < y\}$. Since $x < m$ and $m < y$, these are nonempty and they are bounded, because +of the restrictions $x < a < m$ and $m < b < y$. So, there exists $k \in X$, that is not rational such that +$x < k < m$ and there exists $h \in Y$ that is not rational such that $m < h < y$. Pick either $k$ or $h$ as $i$, +since $x < k < m < h < y$. \qed + +\exercise* +\begin{tcolorbox} + Let $E \subset (0,1)$ be the set of all real numbers with decimal representation using only the digits 1 and 2: + \begin{equation} + E := \{x \in (0,1) : \forall j \in \N, \exists d_j \in \{1,2\} \text{ such that } x = 0.d_1d_2...\} + \end{equation} + Prove that $|E| = |\mathcal{P}(\N)|$. +\end{tcolorbox} \end{document}