Answer:
3π/2
Explanation:
It may help you to realize that the (x, y) coordinates of the point on the unit circle are ...
(x, y) = (cos(θ), sin(θ))
Since you want sin(θ) = -1, look for the point on the unit circle that has a y-value of -1. It is the point (0, -1) at the bottom of the circle, where the angle is shown as ...
θ = 3π/2