cosπ/7cos2π/7cos4π/7cos8π/7=?每步都写
问题描述：
cosπ/7cos2π/7cos4π/7cos8π/7=?每步都写
答
原式=16sinπ/7cosπ/7cos2π/7cos4π/7cos8π/7/(16siπ/7)=8sin2π/7cos2π/7cos4π/7cos8π/7/(16siπ/7)=4sin4π/7cos4π/7cos8π/7/(16siπ/7)=2sin8π/7cos8π/7/(16siπ/7)=sin16π/7/(16siπ/7)=sin2π/7/(1...