Question

已知x的平方+x-1=0,求x的立方-2x+2008的值

Answer 1

x^2+x-1=0 则x^2=1-x x^2+x=1 x^3-2x+2008 =x*x^2-2x+2008 =x*(1-x)-2x+2008 =-x^2-x+2008 =-1+2008 =2007 =2007