9(a-b)平方-(x-y)平方

问题描述:

9(a-b)平方-(x-y)平方

由9(a-b)²-(x-y)²
=[3(a-b)+(x-y)][3(a-b)-(x-y)]
=(3a-3b+x-y)(3a-3b-x+y).