(x-y)的平方-4(x+y)的平方
问题描述：
(x-y)的平方-4(x+y)的平方
因式分解
答
=(x-y)²-[2(x+y)]²
=(x-y+2x+2y)(x-y-2x-2y)
=(3x+y)(-x-3y)
=-(3x+y)(x+3y)