分解因式:(1)9(x-y)的平方+42(x-y)+49
问题描述:
分解因式:(1)9(x-y)的平方+42(x-y)+49
答
9(x-y)的平方+42(x-y)+49
=[3(x-y)]²+2×3(x-y)×7+7²
=[3(x-y)+7]²
=(3x-3y+7)²