4-12(x-y)+9(x-y)² =(2-3x+3y)²

4-12(x-y)+9(x-y)² =(2-3x+3y)²
4-12(x-y)+9(x-y)² =(2-3x+3y)²

4-12(x-y)+9(x-y)² =(2-3x+3y)²
2²-2(x-y)2+[3(x-y)]²=[2-3(x+y)]²
[2-3(x-y)]²=[2-3(x+y)]²
2-3(x-y)=2-3(x+y) 2-3(x-y)=3(x+y)-2
2-3x+3y=2-3x-3y 2-3x+3y=3x+3y-2
3y+3y=0 -3x-3x=-2-2
y=0 -6x=-4

把a＝（x－y）带入，就明白了，手机不方便，勿怪

4-12x+12y+9(x²-2xy+y²）=（2-3x）²+2×（2-3x）×（3y）²
4-12x+12y+9x²-18xy+9y²=（2-3x）²+36y²-54xy²

对啊，没错
原式=[2-3(x-y)]²
=(2-3x+3y)²