已知x^2-x-1=0,求代数式-x^3+2x^2+2009的值

网友回答

x^2-x-1=0,
x^2-x=1.(1)
又有x^2=x+1,
x^3=x^2+x.(2).
-x^3+2x^2+2009
=-x^2-x+2x^2+2009[(2)代入]
=x^2-x+2009
=1+2009[(1)代入]
=2010.