text: Use the fact that angles are the same every 2pi .... in other words 0 = 2pi = 4pi etc., and pi = 3pi = 5pi, etc.  This is because 2pi is the complete rotation of a circle, or 360 degrees.\n\nSo, 17pi is simply the same angle as pi.\n\nSo, tan 17pi = tan pi = 0\n\nSimilarly, 8pi/3 = 8pi/3 - 6pi/3 = 2pi/3\n\nSo, cos 8pi/3 = cos 2pi/3 = -1/2\n\n~ ♥ ~