x等于2分之根号5减1则x的4次方加x的2次方加5x减1~

x=(√5-1)/2
2x=√5-1
2x+1=√5
(2x+1)^2=5
4x^2+4x+1=5
x^2+x-1=0
x^2=1-x
x^4=(1-x)^2=1-2x+x^2=1-2x+1-x=2-3x
x^4+x^2+5x-1
=(2-3x)+(1-x)+5x-1
=2+x
=(√5+3)/2