问题描述： cos5分之π×cos5分之2π 1个回答 分类：数学 2014-10-13 问题解答： 我来补答 cos(π/5)cos(2π/5)=[4sin(π/5)cos(π/5)cos(2π/5)]/[4sin(π/5]=[2×2sin(π/5)cos(π/5)×cos(2π/5)]/[4sin(π/5)]=[2sin(2π/5)cos(2π/5)]/[4sin(π/5)]=[sin(4π/5)]/[4sin(π/5)]=[sin(π/5)]/[sin(π/5)]=1/4 展开全文阅读
