cos2π/7×cos4π/7×cos6π/7等于多少?3Q

来源：学生作业学帮网编辑：学帮网时间：2024/05/13 09:00:24

原式=sinπ/7*cos2π/7*cos4π/7*-cosπ/7/sinπ/7 =-1/2sin2π/7*cos2π/7*cos4π/7/sinπ/7 =-1/4sin4π/7*cos4π/7/sinπ/7 =-1/8sin8π/7/sinπ/7 =1/8sinπ/7/sinπ/7 =1/8