Continued Fractions edits

This commit is contained in:
2026-04-13 16:18:23 -07:00
parent 58555e2d23
commit 043736b26e
2 changed files with 12 additions and 12 deletions

View File

@@ -78,7 +78,7 @@ An \textit{infinite continued fraction} is an expression of the form
a_0 + \cfrac{1}{a_1+\cfrac{1}{a_2 + \cfrac{1}{a_3 + \cfrac{1}{a_4 + ...}}}} a_0 + \cfrac{1}{a_1+\cfrac{1}{a_2 + \cfrac{1}{a_3 + \cfrac{1}{a_4 + ...}}}}
\] \]
where $a_0, a_1, a_2, ...$ are in $\mathbb{Z}^+_0$. where $a_0, a_1, a_2, ...$ are in $\mathbb{Z}^+_0$.
To prove that this expression actually makes sense and equals a finite number Showing that this expression converges to a finite number
is beyond the scope of this worksheet, so we assume it for now. is beyond the scope of this worksheet, so we assume it for now.
This is denoted $[a_0, a_1, a_2, ...]$. This is denoted $[a_0, a_1, a_2, ...]$.
@@ -133,7 +133,7 @@ A few examples are below. We denote the repeating sequence with a line.
\problem{} \problem{}
\begin{itemize} \begin{itemize}
\item Show that $\sqrt{2} = [1, \overline{2}]$. \item Show that $\sqrt{2} = [1, \overline{2}]$.
\item Show that $\sqrt{5} = [1, \overline{4}]$. \item Show that $\sqrt{5} = [2, \overline{4}]$.
\end{itemize} \end{itemize}
\hint{use the same strategy as \ref{irrational} but without a calculator.} \hint{use the same strategy as \ref{irrational} but without a calculator.}
@@ -159,7 +159,7 @@ Express the following continued fractions in the form $\frac{a+\sqrt{b}}{c}$ whe
\problem{Challenge II} \problem{Challenge II}
Let $\alpha = [~a_0,~ ...,~ a_r,~ \overline{a_{r+1},~ ...,~ a_{r+p}}~]$ be any periodic continued fraction. \par Let $\alpha = [~a_0,~ ...,~ a_r,~ \overline{a_{r+1},~ ...,~ a_{r+p}}~]$ be any periodic continued fraction. \par
Prove that $\alpha$ is of the form $\frac{a+\sqrt{b}}{c}$ for some integers $a,b,c$ where $b$ is not a perfect square. Show that $\alpha$ is of the form $\frac{a+\sqrt{b}}{c}$ for some integers $a,b,c$ where $b$ is not a perfect square.
@@ -168,7 +168,7 @@ Prove that $\alpha$ is of the form $\frac{a+\sqrt{b}}{c}$ for some integers $a,b
\problem{Challenge III} \problem{Challenge III}
Prove that any number of the form $\frac{a+\sqrt{b}}{c}$ where $a,b,c$ are integers Show that any number of the form $\frac{a+\sqrt{b}}{c}$ where $a,b,c$ are integers
and $b$ is not a perfect square can be written as a periodic continued fraction. and $b$ is not a perfect square can be written as a periodic continued fraction.

View File

@@ -65,7 +65,7 @@ Verify the recursive formula for $1\leq j\leq 3$ for the convergents $C_j$ of: \
\problem{Challenge IV}<rec> \problem{Challenge IV}<rec>
Prove that $p_n = a_np_{n-1} + p_{n-2}$ and $q_n = a_nq_{n-1} + q_{n-2}$ by induction. Show that $p_n = a_np_{n-1} + p_{n-2}$ and $q_n = a_nq_{n-1} + q_{n-2}$ by induction.
\begin{itemize} \begin{itemize}
\item As the base case, verify the recursive formulas for $n=1$ and $n=2$. \item As the base case, verify the recursive formulas for $n=1$ and $n=2$.
\item Assume the recursive formulas hold for $n\leq m$ and show the formulas hold for $m+1$. \item Assume the recursive formulas hold for $n\leq m$ and show the formulas hold for $m+1$.
@@ -97,7 +97,7 @@ we will show that $p_n q_{n-1} - p_{n-1}q_n = (-1)^{n-1}$.
\problem{Challenge VI} \problem{Challenge V}
Similarly derive the formula $p_nq_{n-2}-p_{n-2}q_n = (-1)^{n-2}a_n$. Similarly derive the formula $p_nq_{n-2}-p_{n-2}q_n = (-1)^{n-2}a_n$.
@@ -141,7 +141,7 @@ We will show that $|\alpha-C_n|<\frac{1}{q_n^2}$.
We are now ready to prove a fundamental result in the theory of rational approximation. We are now ready to prove a fundamental result in the theory of rational approximation.
\problem{Dirichlet's approximation theorem} \problem{Dirichlet's approximation theorem}
Let $\alpha$ be any irrational number. Let $\alpha$ be any irrational number.
Prove that there are infinitely many rational numbers $\frac{p}{q}$ such that $|\alpha - \frac{p}{q}| < \frac{1}{q^2}$. Show that there are infinitely many rational numbers $\frac{p}{q}$ such that $|\alpha - \frac{p}{q}| < \frac{1}{q^2}$.
@@ -154,8 +154,8 @@ Prove that there are infinitely many rational numbers $\frac{p}{q}$ such that $|
\problem{Challenge VII} \problem{Challenge VI}
Prove that if $\alpha$ is \emph{rational}, then there are only \emph{finitely} many rational numbers $\frac{p}{q}$ Show that if $\alpha$ is \emph{rational}, then there are only \emph{finitely} many rational numbers $\frac{p}{q}$
satisfying $|\alpha - \frac{p}{q} | < \frac{1}{q^2}$. satisfying $|\alpha - \frac{p}{q} | < \frac{1}{q^2}$.
@@ -195,8 +195,8 @@ Let $\frac{a}{b}$ and $\frac{c}{d}$ be consecutive elements of the Farey sequenc
\problem{Challenge VIII}<farey> \problem{Challenge VII}<farey>
Prove that $bc-ad=1$ for $\frac{a}{b}$ and $\frac{c}{d}$ consecutive rational numbers in Farey sequence of order $n$. Show that $bc-ad=1$ for $\frac{a}{b}$ and $\frac{c}{d}$ consecutive rational numbers in Farey sequence of order $n$.
\begin{itemize}[itemsep=2mm] \begin{itemize}[itemsep=2mm]
\item In the plane, draw the triangle with vertices (0,0), $(b,a)$, $(d,c)$. \item In the plane, draw the triangle with vertices (0,0), $(b,a)$, $(d,c)$.
@@ -237,7 +237,7 @@ $|\alpha - \frac ab| \geq |\alpha - \frac{p_n}{q_n}|$
\problem{Challenge X} \problem{Challenge VIII}
Prove the following strengthening of Dirichlet's approximation theorem. Prove the following strengthening of Dirichlet's approximation theorem.
If $\alpha$ is irrational, then there are infinitely many rational numbers If $\alpha$ is irrational, then there are infinitely many rational numbers
$\frac{p}{q}$ satisfying $|\alpha - \frac pq| < \frac{1}{2q^2}$. $\frac{p}{q}$ satisfying $|\alpha - \frac pq| < \frac{1}{2q^2}$.