计算 (x-y)²-(x+y)(x-y)

问题描述:

计算 (x-y)²-(x+y)(x-y)

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