cosπ/3,单词大作战cos

sinx cosx tanx的特殊值 比例cos2π/3=1这样的
cosπ/4=?
求证:cos4π/3
求值:cos(π/11)cos(2π/11)cos(3π/11)cos(4π/11)cos(5π/11)
2cos(π 30°)呢