解答：在直角坐标系中，作∠AOB=7π/6 (第三象限)易知∠AOB的终边和单位圆的交点坐标是(-√3/2,-1/2)∴ sin(7π/6)=-1/2 cos(7π/6)=-√3/2 tan(7π/6)=-√3/3
