text: help with trigonometry? using the periodic properties of trigonometric functions, find the exact value of the expression:   tan 17pi  cos 8pi/3 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.  so, 17pi is simply the same angle as pi.  so, tan 17pi = tan pi = 0  similarly, 8pi/3 = 8pi/3 - 6pi/3 = 2pi/3  so, cos 8pi/3 = cos 2pi/3 = -1/2  ~ ♥ ~