cos9/π.cos9/2π.cos9/3π.cos9/4π等于多少!
问题描述:
cos9/π.cos9/2π.cos9/3π.cos9/4π等于多少!
答
cos9/3π=2/1
cos9/π·cos9/2π·cos9/4π
=8sin9/π·cos9/π·cos9/2π·cos9/4π÷8sin9/π
=4sin9/2π·cos9/2π·cos9/4π÷8sin9/π
=2sin9/4π·cos9/4π÷8sin9/π
=sin9/8π÷8sin9/π
=sin9/π÷8sin9/π
=8/1
∴原式=16/1