f(x - 1/x) = 1/ ( x² +1/x²) = 1/ [(x-1/x)² + 2 ]f(x) = 1/ ( x² +2)
F=x^2/(x^4+1)=1/(x^2+1/x^2)=1/(x^2+1/x^2-2+2)=1/[(x-1/x)^2+2]将x-1/x换成xf=1/(x^2+2)
