(x-y)的三次方+9(x-y)-6(x-y)的平方
问题描述：
(x-y)的三次方+9(x-y)-6(x-y)的平方
答
(x-y)^3+9(x-y)-6(x-y)^2
=(x-y)[(x-y)^2-6(x-y)+9]
=(x-y)[(x-y)-3]^2
=(x-y)(x-y-3)^2