问题描述： 1/30+1/42+1/56+1/72= 1个回答 分类：数学 2014-10-19 问题解答： 我来补答 原式=1/(5×6)+1/(6×7)+1/(7×8)+1/(8×9)=(6-5)/(5×6)+(7-6)/(6×7)+(8-7)/(7×8)+(9-8)/(8×9)=6/(5×6)-5/(5×6)+7/(6×7)-6/(6×7)+8/(7×8)-7/(7×8)+9/(8×9)-8/(8×9)=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9=1/5-1/9=9/45-5/45=4/45 展开全文阅读
