倍角公式与和角公式化简或求值cos π/17 * cos 2π/17 * cos 4π/17 * cos 8π/17

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倍角公式与和角公式
化简或求值cos π/17 * cos 2π/17 * cos 4π/17 * cos 8π/17

分子分母同乘以16sin(π/17)即可利用二倍角公式化简
cos(π/17)cos(2π/17)cos(4π/17)cos(8π/17)
=[16sin(π/17)cos(π/17)cos(2π/17)cos(4π/17)cos(8π/17)]/16sin(π/17)
=[8sin(2π/17)cos(2π/17)cos(4π/17)cos(8π/17)]/16sin(π/17)
=[4sin(4π/17)cos(4π/17)cos(8π/17)]/16sin(π/17)
=[2sin(8π/17)cos(8π/17)]/16sin(π/17)
=sin(16π/17)/16sin(π/17)
=1/16

化简求值sin(-20/3π)cos(43/6π)+sin(35/6π)cos-(17/3π) 二倍角公式题求值：1/2-cos²π/8 8sin(π/32)cos(π/32)cos(π/16)cos(π/8),求值求值cos5π/8*cosπ8 求值：cos（25π /4） cos(π/32)*cos(π/16)*cos(π/8)= 利用二倍角公式求值sin(π/12)cos(π/12) cos（－17/3π）＝? 求值：sin(π/12)+cos(π/12) 求SINπ/64 COSπ/64 COSπ/32 COSπ/16 COSπ/8 已知cos（π4 【紧急求助】计算:cosα+cos(2π/3 +α)+cos（4π/3 +α）