解
(y²-xy)/(x²-y²)
=y(y-x)/(x+y)(x-y)
=-y/(x+y)

(2x²-2y²)/(x²+2xy+y²)
=2(x+y)(x-y)/(x+y)²
=2(x-y)/(x+y)

x,y是什么值