因为x^2-x-1=0 所以X^2-1=X
2006+2X-X^3
=2006-X(X^2-2)
=2006-X(X^-1-1)
=2006-X(X-1)
=2006-(X^2-X)
因为x^2-x-1=0 所以X^2-X=1
接上面 =2006-1=2005