I know how to do cos(5pi/6) and any question like it.

But I don't know how to do sin, cos, tan, csc, cot, sec, of angles like 0 (0pi/12), 90 (3pi/12), 180 (6pi/12), 270 (9pi/12), 360 (12pi/12), 450 (15pi/12), etc.

Can somebody show me how?

ALso, I don't understand why cos (0pi/12) = 0, too. Or why some are undefined.