you start at 0 on the unit circle the cos of 0 =1, but at cos 0 there is no angle at all so there is no y value so at cos 0 y=0, 180 is the opposite direction of the starting point which is 0 so the x value of cos180= -1 but there is still no upward or downward angle ie.. y value. so the y value = 0 at 0 and 180. answer is 0
