由x^2-3x-1=0得
3x^2-9x=3 (1)
x^3-3x^2-x=0 (2)
2(x^3-3x^2-x)=0
2x^3-6x^2-2x=0
原式
=2x^3-3x^2-11x-8
=2x^3-3x^2-11x-8-(2x^3-6x^2-2x)
=3x^2-9x-8
=3-8
=-5
由x^2-3x-1=0得
3x^2-9x=3 (1)
x^3-3x^2-x=0 (2)
2(x^3-3x^2-x)=0
2x^3-6x^2-2x=0
原式
=2x^3-3x^2-11x-8
=2x^3-3x^2-11x-8-(2x^3-6x^2-2x)
=3x^2-9x-8
=3-8
=-5