因式分解x^2(y-x)+81(z-y)
问题描述：
因式分解x^2(y-x)+81(z-y)
答
x^2(y-x)+81(z-y)
=x^2(y-x)-81(y-x)
=(x^2-81)(y-x)
=(x-9)(x+9)(y-x)