x^2+x-1=0,
x^2=1-x
在它的两边同时乘以x,得
x^3=x-x^2=x-(1-x)=2x-1
所以
x^3+2x^2+2006
=2x-1+2(1-x)+2006
=2x-1+2-2x+2006
=2007