an=1/((2n-1)(2n+1))=(1/2)*((1/(2n-1))-(1/(2n+1)))Sn=(1/2)(1-(1/3)+(1/3)-(1/5)+……+(1/(2n-1))-(1/(2n+1)))=(1/2)(1-(1/(2n+1)))=n/(2n+1)
