已知x+1/x=4,则x^2/(x^4+x^2+1)=?
(x^4+x^2+1)/x^2
=x^2+1+1/x^2
=x^2+1/x^2+1
=(x+1/x)^2-2+1
=4^2-1
=16-1
=15
所以：x^2/(x^4+x^2+1)=1/15.