Sin (13pi/2) in periodic function

Answer: 1

13pi/2 can be simplified onto 6 pi/2, so it goes around the unit circle 6 times and left with pi/2. the coordinates of pi/2 is (0,1). the trigonometric function sin is y/r. since r is always 1 on the unit circle, the answer is the y value, in this case it is 1.