4加12乘(x-y)加9(x-y)的平方

4加12乘(x-y)加9(x-y)的平方


4+12×(x-y)+9(x-y)^2
=2^2+2×2×3(x-y)+[3(x-y)]^2
=[2+3(x-y)]^2
=(3x-3y+2)^2