(1)Sn=n^2+n那么an=Sn-Sn-1=2n(2)bn=1/[2n*2(n+1)]=1/4*1/[n(n+1)]=1/4*[1/隐扮唯n-1/(n+1)],上一步叫做裂灶培项,通分可知是正确的。bn的前n项和为1/4[1-1/缺禅2+1/2-1/3+`````````````+1/n-1/(n+1)]=n/4(n+1) http://zhidao.baidu.com/question/244348067.html