问题描述： cos五分之π 乘以cos五分之二π 1个回答 分类：数学 2014-12-14 问题解答： 我来补答 原式=2sin(π/5)cos(π/5)cos(2π/5)/[2sin(π/5)]=sin(2π/5)cos(2π/5)/[2sin(π/5)]=2sin(2π/5)cos(2π/5)/[4sin(π/5)]=sin(4π/5)/[4sin(π/5)]=sin(π-π/5)/[4sin(π/5)]=sin(π/5)/[4sin(π/5)]=1/4 展开全文阅读
