Question 35263
Well, lets think about this:
{{{x^2=y^2=25}}}
{{{sqrt(x^2)=sqrt(y^2)=sqrt(25)}}}
{{{x=y=5}}}
Or 
{{{x=y=-5}}}
{{{y-x=1}}}
{{{-5--5=-5+5=0}}}
{{{5-5=0}}}
As you can see it is impossible for both equations to be true. 

hope this helps,
lyra