x+1\x=3等式两边平方得
x^2+1/x^2+2*x*(1/x)=3^2,则^2+1/x^2=9-2=7
(x^2)/(x^4+x^2+1)
=1/(x^2+1+1/x^2)
=1/(7+1)
=1/8