t=x+1/x, |t|>=2
t^2-2=x^2+1/x^2
2t^2-4-3t-1=0
2t^2-3t-5=0
(2t-5)(t+1)=0
t=5/2, t=-1(舍去)
x+1/x=5/2
x=2 or 1/2