(x+y)(x+y)-x(x+y)急啊啊啊啊,
问题描述：
(x+y)(x+y)-x(x+y)急啊啊啊啊,
答
(x+y)(x+y)-x(x+y)
=[(x+y)-x](x+y)
=y(x+y)为什么啊