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
答
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