已知x^2-3x-9=0 求x^3-6x^2的值

问题描述:

已知x^2-3x-9=0 求x^3-6x^2的值

x^2-3x-9=0
x^2-3x=9
x^3-3x^2=9x,x^2=3x+9
x^3-6x^2=x^3-3x^2-3x^2=9x-3x^2=9x-3(3x+9)=9x-9x-27=-27