cos225°=cos(-225°)=cos(360°-225°)=cos135°=-√2/2
sin11/3π=cos(4π-1/3π)=cos(-1/3π)=cos1/3π=1/2
sin(-16/3π)=sin(-6π+2/3π)=sin2/3π=sin(π-1/3π)=sin1/3π=√3/2
cos(-2040°)=cos(-6*360°+120°)=cos120°=-1/2