cos九分之派乘以cos九分之二派乘以cos九分之三派乘以cos九分之四派.cos七分之π乘以cos七分之二π乘以cos七分之三π

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cos九分之派乘以cos九分之二派乘以cos九分之三派乘以cos九分之四派.cos七分之π乘以cos七分之二π乘以cos七分之三πcos九分之派乘以cos九分之二派乘以cos九分之三派乘以cos九分之

cos九分之派乘以cos九分之二派乘以cos九分之三派乘以cos九分之四派.cos七分之π乘以cos七分之二π乘以cos七分之三π
cos九分之派乘以cos九分之二派乘以cos九分之三派乘以cos九分之四派.
cos七分之π乘以cos七分之二π乘以cos七分之三π

cos九分之派乘以cos九分之二派乘以cos九分之三派乘以cos九分之四派.cos七分之π乘以cos七分之二π乘以cos七分之三π
是求值吗? 若是这样,则方法如下:
原式=cos(2π/14)cos(4π/14)cos(6π/14)
  =2sin(2π/14)cos(2π/14)cos(4π/14)cos(6π/14)/[2sin(2π/14)]
  =sin(4π/14)cos(4π/14)cos(6π/14)/[2sin(π/7)]
  =2sin(4π/14)cos(4π/14)cos(6π/14)/[4sin(π/7)]
  =sin(8π/14)cos(6π/14)/[4sin(π/7)]
  =sin(π/2+π/14)cos(π/2-π/14)/[4sin(π/7)]
  =2cos(π/14)sin(π/14)/[8sin(π/7)]
  =sin(π/7)/[8sin(π/7)]
  =1/8
注:若你的意图不是我所猜测的那样,则请你补充说明.