作业帮求值：cos2π/7 * cos4π/7 * cos6π/7
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求值：cos2π/7 * cos4π/7 * cos6π/7
求值：cos2π/7 * cos4π/7 * cos6π/7
求值：cos2π/7 * cos4π/7 * cos6π/7
原式=[sin(2π/7)*cos(2π/7)*cos(4π/7)*cos(6π/7)]/[sin(2π/7)]
=[sin(4π/7)*cos(4π/7)*cos96π/7)]/[2sin(2π/7)]
=[sin(8π/7)*cos(6π/7)]/[4sin(2π/7)]
=[sin(π+π/7)*cos(π-π/7)]/[4sin(2π/7)]
=+[sin(π/7)*cos(π/7)]/[4sin(2π/7)]
=sin(2π/7)/[8sin(2π/7)]
=1/8
求值：cos2π/7 * cos4π/7 * cos6π/7
求值:cos2π/7cos4π/7cos8π/7
求值：Cos2/7π＋Cos4/7π＋Cos6/7π
求值:cosπ/7·cos2π/7·cos4π/7
求值cos2π/9*cos4π/9*8π/9
求值cos2π/9cos4π/9cos8π/9
求值:cosπ/7cos2π/7cos3π/7cos4π/7cos5π/7cos6π/7
cos2/7π*cos4/7π*cos6/7π=?
cosπ/7cos2/7πcos4/7π=
cos2π/7+cos4π/7+6π/7=
cos2π/7cos4π/7cos6π/7=?
cos2π/7+cos4π/7+cos6π/7=
cos2/7π+cos4/7π+cos6/7=
求值：cosπ/17cos2π/17cos4π/17cos8π/17
求值cosπ/5cos2π/5cos4π/5cos8π/5
求值：cos2∏/7*cos4∏/7*cos8∏/7请尽快作答,
三角函数求值高手进求值：cos2π/7+cos4π/7+cos6π/7提示：乘以2sin2π/7,化简后再除下去.不要用别的方法做!构造法我会的 就是这个方法算不出来
化简sin π/7(cos2π/7+cos4π/7+cos6π/7)