f(x)+f(1/x)=x^2/(1+x^2) +1/x^2/(1+1/x^2)=x^2/(1+x^2) + 1/(1+x^2) (分子分母都乘以x^2)=(x^2+1)/(1+x^2)=1所以f(2)+f(1/2) =1f(3)+f(1/3) =1f(4)+f(1/4) =1f(1)=1/2累加为 7/2