cos(7π/6)=cos(π+π/6)=-cos(π/6)=-√3/2 。
cos7/6 π＝cos(π+π/6)=-cosπ/6=-√3/2
cos7/6 π=cos(-1/6π)=-√3/2
cos(7π/6)=cos(π+π/6) =-cos(π/6) =-√3/2
=-√3/2 。
