cosπ/5*cos2π/5 =(2sinπ/5*cosπ/5*cos2π/5)/(2sinπ/5) =(sin2π/5

问题描述:

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?
1个回答 分类:数学 2014-11-16

问题解答:

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