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.

1个回答

  • 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.