when working with polar coordinates, remember that there are several ways to represent the same point. For example, the point (2, Pi) is the same as the point (-2, 0), (-2, -Pi), (2, 0).
You can check this by converting the polar coordinates to rectangular coordinates.
If the polar coordinate is represented as (r, A) where r is the radius and A is the angle, then
x = rcos(A), y = rsin(A)
Using the above example,
y= 2sin(Pi) converts to (-2,0) in rectangular coordinates
Likewise using the same formula for the polar coordinates (-2, 0), (-2, -Pi), (2, 0) also convert to (-2, 0) in rectangular coordinates.