x³一11x²十31一21因式分解
问题描述：
x³一11x²十31一21因式分解
答
x³一11x²十31x一21
=x³一6x²十9x一5x²十22x一21
=x(x-3)^2-(5x-7)(x-3)
=(x-3)(x^2-3x-5x+7)
=(x-3)(x^2-8x+7)