问题描述: 1/(1*4)+1/(4*7)+1/(7*10)+……+1/[(3n-2)(3n+1)]求和 1个回答 分类: 数学 2014-11-07 问题解答: 我来补答 1/(1*4)+1/(4*7)+1/(7*10)+……+1/[(3n-2)(3n+1)]=3(1-1/4+1/4-1/7+...+1/(3n-2)-1/(3n+1))=3*(1-1/(3n+1))=9n/3n+1 展开全文阅读