因式分解：4+ 12（x-y)+9(x-y)(x-y)
问题描述：
因式分解：4+ 12（x-y)+9(x-y)(x-y)
快
答
4+ 12(x-y)+9(x-y)²
=[3(x-y)]²+2×[3(x-y)]×2+2²
=[3(x-y)+2]²
=(3x-3y+2)²