storm oracle数据源:求值cos2π/9cos4π/9cos8π/9
来源:百度文库 编辑:高考问答 时间:2024/05/12 12:17:00
cos2π/9cos4π/9cos8π/9
分子分母同时乘以sin2π/9,
就行了
(8sin2π/9cos2π/9cos4π/9cos8π/9)/8sin2π/9
分子变为sin16π /9
所以为-1/8
cos2π/9cos4π/9cos8π/9=(sin2π/9*cos2π/9cos4π/9cos8π/9)/sin2π/9=((1/2)*sin4π/9*cos4π/9*cos8π/9)/sin2π/9=(1/8sin16π/9)/(sin2π/9)
因为sin16π/9=-sin2π/9
所以=g-
1/729
由于cos2π cos4π cos8π的值都为1.所以cos2π/9cos4π/9cos8π/9=1/9/9/9=1/729.
1/729
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