3x^3-x-1=0
3X^3=(X+1)
所以
9x^4+12x^3-3x^2-7x+2008
=3x（x+1）+4(x+1)-3x^2-7x+2008
=3x^2+3x+4x+4-3x^2-7x+2008
=4+2008
=2012