sin(7π/6)=sin(π+π/6)=-sin(π/6)=-1/2
cos(7π/6)=cos(π+π/6)=-cos(π/6)=-√3/2
tan(7π/6)=tan(π+π/6)=tan(π/6)=√3/3
7π/6在第三象限,sin7π/6