一1/x+x=(x^2+1)/x=3x/x=3
1/x^2+x^2=(1/x+x)^2-2=9-2=7
x+1/x-1=8
x=9/7
(9/7)^2+k9/7-2=0
k=17/63
x9/7=-2
x=-14/9