cosπ/9cos2π/9cos23π/9
答案:1 悬赏:30 手机版
解决时间 2021-11-29 16:41
- 提问者网友：夢醒日落
- 2021-11-28 22:57
cosπ/9cos2π/9cos23π/9
最佳答案
- 五星知识达人网友：一秋
- 2021-11-28 23:35
cosπ/9cos2π/9cos23π/9
=[2sinπ/9cosπ/9cos2π/9cos23π/9]/2sinπ/9
=[sin2π/9cos2π/9cos(2π+5π/9)]/2sinπ/9
=[sin4π/9cos5π/9]/4sinπ/9
=-[sin4π/9cos4π/9]/4sinπ/9
=-(sin8π/9)/8sinπ/9
=-(sinπ/9)/8sinπ/9
=-1/8
=[2sinπ/9cosπ/9cos2π/9cos23π/9]/2sinπ/9
=[sin2π/9cos2π/9cos(2π+5π/9)]/2sinπ/9
=[sin4π/9cos5π/9]/4sinπ/9
=-[sin4π/9cos4π/9]/4sinπ/9
=-(sin8π/9)/8sinπ/9
=-(sinπ/9)/8sinπ/9
=-1/8
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