S(x)=∑x^(4n+1)/(4n+1), 则S‘(x)=∑x^(4n)=1/(1-x^4), S(x)=∫<0,x>dt/(1-t^4) = (1/4)∫<0,x>[1/(1-t)+1/(1+t)+2/(1+t^2)]dt = (1/4)[ln(1+t)-ln(1-t)+2arctant]<0,x> = (1/4)ln[(1+x)/(1-x)]+(1/2)arctanx.-1
