(x-1/x)^2
=x^2-2+1/x^2
=(x+1/x)^2-4
设x+1/x=t
t^2-4-9/2t+9=0
t^2-9/2t+5=0
2t^2-9t+10=0
(2t-5)(t-2)=0
t1=5/2 t2=2
x+1/x=5/2
2x^2+2=5x
2x^2-5x+2=0
(2x-1)(x-2)=0
x1=1/2 x2=2
x+1/x=2
x^2+1=2x
x^2-2x+1=0
(x-1)^2=0
x=1