求cosπ/9*cos2π/9*cos4π/9的值如题
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解决时间 2021-01-25 04:54
- 提问者网友：几叶到寒
- 2021-01-24 08:06
求cosπ/9*cos2π/9*cos4π/9的值如题
最佳答案
- 五星知识达人网友：山河有幸埋战骨
- 2021-01-24 09:36
利用2倍角公式cosπ/9*cos2π/9*cos4π/9=[sinπ/9*cosπ/9*cos2π/9*cos4π/9]/sinπ/9=[1/2sin2π/9*cos2π/9*cos4π/9]/sinπ/9=[1/4sin4π/9*cos4π/9]/sinπ/9=[1/8sin8π/9]/sinπ/9=[1/8sinπ/9]/[sinπ/9]=1/8======以下答案可供参考======供参考答案1:cosπ/9*cos2π/9*cos4π/9=2sinπ/9*cosπ/9*cos2π/9*cos4π/9/(2sinπ/9)=sin2π/9*cos2π/9*cos4π/9/(2sinπ/9)=2sin2π/9*cos2π/9*cos4π/9/(4sinπ/9)=sin4π/9*cos4π/9/(4sinπ/9)=2sin4π/9*cos4π/9/(8sinπ/9)=sin8π/9/(8sinπ/9)=sin(π-π/9)/(8sinπ/9)=sinπ/9/(8sinπ/9)=1/8供参考答案2:(sinπ/9*cosπ/9*cos2π/9*cos4π/9)/(sinπ/9)=(sin8π/9)/8(sinπ/9) =(sinπ/9)/8(sinπ/9)=1/8
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- 1楼网友：野味小生
- 2021-01-24 10:35
这个问题的回答的对
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