Let $S_1$ and $S_2$ be sets of points on the coordinate plane $\mathbb{R}^2$ defined as follows \[S_1={(x,y)\in \mathbb{R}^2:|x+|x||+|y+|y||\le 2}\] \[S_2={(x,y)\in \mathbb{R}^2:|x-|x||+|y-|y||\le 2}\] Find the area of the intersection of $S_1$ and $S_2$
Problem
Source:
Tags: analytic geometry, geometry
MathStudent2002
04.06.2014 06:44
We consider 4 cases:
Case 1$x\geq0$, $y\geq0$.
We have:
S1$2x+2y\leq2$, so $x+y\leq1$.
S2$0+0\leq$, so $0\leq2$.
We then have the area bounded by $x+y\leq1$, and the $x$ and $y$ axis, so we get $\frac{1\cdot1}{2}=\frac{1}{2}$.
Case 2$x<0$, $y\geq0$.
We have:
S1$2y\leq2$, so $y\leq1$
S2$-2x\leq2$, so $x\geq-1$
We then have a 1x1 square, with an area of $1\cdot1=1$.
Case 3$x<0$, $y<0$.
We have:
S1$0+0\leq2$, so $0\leq2$
S2$-2x-2y\leq2$, so $x+y\geq-1$
We then have a triangle with area $\frac{1\cdot1}{2}=\frac{1}{2}$.
Case 4$x\geq0$, $y<0$.
S1We have $2x\leq2$, so $x\leq0$
S2We have $-2y\leq2$, so $y\geq-1$
We then have a 1x1 square, which has area $1\cdot1=1$.
Our total, then, is $\frac{1}{2}+1+\frac{1}{2}+1=\boxed{3}$
Zimbalono
05.06.2014 17:44
[asy][asy]
size(8cm);import graph;
path p=(-3,1)--(0,1)--(1,0)--(1,-3);
path q=(-1,3)--(-1,0)--(0,-1)--(3,-1);
fill(buildcycle(p,q),gray(.9));
draw(p^^q,blue+dashed);
xlimits(-3,3);ylimits(-3,3);yaxis("$y$",RightTicks());xaxis("$x$",Ticks());
draw((-1,0)--(1,0)^^(0,1)--(0,-1));
[/asy][/asy]