4十12(x一y)+9(x+y)^2
问题描述：
4十12(x一y)+9(x+y)^2
答
=9(x+y)²-12(x+y)+4
=[3(x+y)-2]²
答
=[3(x+y)-2]²
答
4+12x-12y+9x^2+18xy+9y^2是不是？
答
4十12(x一y)+9(x+y)^2=[3(x+y)-2]²
答
=[3(x-y)^2+2]^2+36xy
答
=9(x+y)²-12(x+y)+4
=[3(x+y)-2]²
详帮助你理可以当(x+y)为一个值z
那么其实就是9z²+4-12z
( 3z-2)²
最后将z带入就的=[3(x+y)-2]²
答
12x+12y+9x2+2xy+9y2