cos2π/7cos4π/7cos8π/7要过程
问题描述:
cos2π/7cos4π/7cos8π/7要过程
答
8sin2π/7cos2π/7cos4π/7cos8π/7/(8sin2π/7)
=4sin4π/7cos4π/7cos8π/7/(8sin2π/7)
=2sin8π/7cos8π/7/(8sin2π/7)
=sin16π/7/(8sin2π/7)
=sin2π/7/(8sin2π/7)
=1/8