# Difference between revisions of "2001 AMC 10 Problems/Problem 20"

## Problem

A regular octagon is formed by cutting an isosceles right triangle from each of the corners of a square with sides of length $2000$. What is the length of each side of the octagon?

$\textbf{(A)} \frac{1}{3}(2000) \qquad \textbf{(B)} {2000(\sqrt{2}-1)} \qquad \textbf{(C)} {2000(2-\sqrt{2})} \qquad \textbf{(D)} {1000} \qquad \textbf{(E)} {1000\sqrt{2}}$

## Solution

$[asy] draw((0,0)--(0,10)--(10,10)--(10,0)--cycle); draw((0,7)--(3,10)); draw((7,10)--(10,7)); draw((10,3)--(7,0)); draw((3,0)--(0,3)); label("x",(0,1),W); label("x\sqrt{2}",(1.5,1.5),NE); label("2000-2x",(5,0),S);[/asy]$

$2000 - 2x = x\sqrt2$

$2000 = x(2 + \sqrt2)$

$x = \frac {2000}{2 + \sqrt2} =x = \frac {2000(2 - \sqrt2)}{(2 + \sqrt2)(2 - \sqrt2)}= \frac {2000(2 - \sqrt2)}{2} = 1000(2 - \sqrt2)$

$x\sqrt2 = 1000(2\sqrt {2} - 2) = \boxed{\textbf{(B)}\ 2000(\sqrt2-1)}$.

~edited by qkddud~

 2001 AMC 10 (Problems • Answer Key • Resources) Preceded byProblem 19 Followed byProblem 21 1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 All AMC 10 Problems and Solutions