4+12(x-y)+9(x-y)^

问题描述:

4+12(x-y)+9(x-y)^

=(2+3(x-y))^2
=(3x-3y+2)^2

21x-21y+4

4+12(x-y)+9(x-y)^2完全平方公式
=[2+3(x-y)]^2
=(2+3x-3y)^2