cos(（-19/6）派)=多少求项解过程

题目

cos(（-19/6）派)=多少求项解过程

答案

-19π/6=-4π+5π/6
cos(-19π/6)=cos(-4π+5π/6)=cos(5π/6)=cos(π-π/6)=-cosπ/6=-√3/2