f(x)=x^3-2x^2-x+2
=x³-x²-x²+x-2x+2
=x²(x-1)-x(x-1)-2(x-1)
=(x-1)(x²-x-2)
=(x-1)(x-2)(x+1)
零点:x=1,2,-1
图像自己画