Question

$( frac{x+y}{x-y} + frac{x-y}{x+y} ) : frac{xy}{ x^{2} y^{2} }$

Answer 1

$frac{(x+y)^2-(x-y)^2}{(x-y)(x+y)}:frac{xy}{x^2-y^2}= frac{x^2+2xy+y^2-x^2+2xy-y^2}{x^2-y^2}* frac{x^2-y^2}{xy} = frac{4xy}{x^2-y^2}* frac{x^2-y^2}{xy} \ =4$