一道代数题9(x
9(x-y)^2+12(x^2-y^2）+4(x+y)^2因式分解　　　　　　（要具体答案）
[3(x-y)]^2+2*3*2(x-y)(x+y)+[2(x+y)]^2 =[3(x-y)+2(x+y)]^2 =(3x-3y+2x+2y)^2 =(5x-y)^2