已知A=(x-y)方-(x-y)(x+y) B=((x+y)(x-2y)+2y方)除以x x=2 y=2 比较A.B的值大小,小明说A大,小华说B大,

题目

已知A=(x-y)方-(x-y)(x+y) B=((x+y)(x-2y)+2y方)除以x x=2 y=2 比较A.B的值大小,小明说A大,小华说B大,
判断谁对

答案

A=(x-y)方-(x-y)(x+y)
=（x-y）(x-y-x-y)
=-2y(x-y)
B=((x+y)(x-2y)+2y方)除以x
=(x^2-xy-2y^2+2y^2)/x
=x-y
x=2 y=2
A=-2*2（2-2）=0
B=2-2=0
所以A=B