数列{an}通项公式为an=1/4n^2-1,求数列{an}的前n项和

an=1/(2n+1)(2n-1)=(1/2)[1/(2n-1)-1/(2n+1)]
所以Sn=(1/2)*(1-1/3)+(1/2)*(1/3-1/5)+(1/2)(1/5-1/7)……+(1/2)[1/(2n-1)-1/(2n+1)]
=(1/2)[1-1/(2n+1)]
=n/(2n+1)