What's sine of 3 pi over 2? If you visualize the unit circle real fast, 3 pi over 2 is going all the way 3 4ths around the unit circle. So it's right over there. So the sine is the y-coordinate on that unit circle. So it's negative 1. So this right over here is negative 1. This right over here, sine of pi over 2, pi over 2 is just going straight up like that.