我是想知道解这样子的题是怎样的解题思路
cosπ/9cos2π/9cos3π/9cos4π/9=?
答案:2 悬赏:60 手机版
解决时间 2021-08-20 04:24
- 提问者网友：容嬷嬷拿针来
- 2021-08-20 01:24
最佳答案
- 五星知识达人网友：我住北渡口
- 2021-08-20 02:46
(cosπ/9)(cos2π/9)(cos3π/9)(cos4π/9)
=(sinπ/9)(cosπ/9)(cos2π/9)(cosπ/3)(cos4π/9)/(sinπ/9)
=(sin2π/9)(cos2π/9)(cos4π/9)/[4(sinπ/9)]
=(sin4π/9)(cos4π/9)/[8(sinπ/9)]
=(sin8π/9)/[16(sinπ/9)]
=(sinπ/9)/[16(sinπ/9)]
=1/16
=(sinπ/9)(cosπ/9)(cos2π/9)(cosπ/3)(cos4π/9)/(sinπ/9)
=(sin2π/9)(cos2π/9)(cos4π/9)/[4(sinπ/9)]
=(sin4π/9)(cos4π/9)/[8(sinπ/9)]
=(sin8π/9)/[16(sinπ/9)]
=(sinπ/9)/[16(sinπ/9)]
=1/16
全部回答
- 1楼网友：渡鹤影
- 2021-08-20 03:27
(cosπ/9)(cos2π/9)(cos3π/9)(cos4π/9)
=(sinπ/9)(cosπ/9)(cos2π/9)(cosπ/3)(cos4π/9)/(sinπ/9)
=(sin2π/9)(cos2π/9)(cos4π/9)/[4(sinπ/9)]
=(sin4π/9)(cos4π/9)/[8(sinπ/9)]
=(sin8π/9)/[16(sinπ/9)]
=(sinπ/9)/[16(sinπ/9)]
=1/16
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