(x-1)(x2+x-8)
令f(x)=x3-9x+8
f(1)=0 说明(x-1)是因式
x2(x-1)+x(x-1)-8(x-1)
=x3-x2+x2-x-8x+8
=(x-1)(x2+x-8)
tip:x2代表x的平方