sin(-1920°)=sin(-1920°+360°*6)=sin(240°)=-√3/2
cos(-1560°)=cos(-1560°+360°*5)=cos(240°)=-1/2
tan(-17π/6)=tan(-17π/6+π*3)=tan(1/6π)=√3/3
sin(-1920°)=sin(-1920°+360°*6)=sin(240°)=-√3/2
cos(-1560°)=cos(-1560°+360°*5)=cos(240°)=-1/2
tan(-17π/6)=tan(-17π/6+π*3)=tan(1/6π)=√3/3