Question

已知x=2分之根号5-1,求代数式2x²+x-1的值？

Answer 1

x=2分之根号5-1
2x²+x-1=2*[(根号5-1)/2]²+(根号5-1)/2-1=(3-根号5)/2,4,x=(根号5-1)/2
2x=根号5-1
2x+1=根号5
(2x+1)^2=5
4x^2+4x+1=5
x^2+x=1
x^3+2x^2-1
=x(x^2+x)+x^2-1
=x+x^2-1
=1-1
=0,2,我不会,0,