(x+y)的平方乘以(x-y)-(x-y)乘以(x的平方+y的平方)
问题描述：
(x+y)的平方乘以(x-y)-(x-y)乘以(x的平方+y的平方)
答
=(x-y)[(x+y)²-(x²+y²)]
=(x-y)(x²+2xy+y²-x²-y²)
=2xy(x-y)