cosπ/5*cos2π/5 =(2sinπ/5*cosπ/5*cos2π/5)/(2sinπ/5) =(sin2π/5*cos2_数学解答

cosπ/5*cos2π/5 =(2sinπ/5*cosπ/5*cos2π/5)/(2sinπ/5) =(sin2π/5*cos2π/5)/(2sinπ/5) =(2sin2π/
低2部咋算的?

人气：486 ℃　时间：2020-01-06 16:08:51

解答

倍角公式
sin2a=2sinacosa
所以2sinπ/5*cosπ/5=sin2π/5是另一部那就是上下同乘以2sinπ/5自己看懂了，嘿嘿