由x^2-x-1=0 得x^2=x+1 x=x^2-1 x^2-x=1
-x^3+2x+2008=-x(x+1)+2(x^2-1)+2008
=-x^2-x+2x^2-2+2008
=x^2-x+2006
=1+2006
=2007再问一道。a的三次方+a-1=0，求代数式a的三次方+2a的二次方+8的值