Question

$frac{x+y}{x-y} - frac{x-y}{x+y}$

Answer 1

(x+y)/(x-y)-(x-y)/(x+y)=((x+y)^2-(x-y)^2)/(x^2-y^2)=(x^2+2xy+y^2-x^2+2xy-y^2)/(x^2-y^2)=4xy/(x^2-y^2)