I am working on this problem. 
I need to find the polar coordinates of point $D$ on the curve. Now since $D$ lies on the negative $y$ axis, $\theta = 3\pi/2$ and I get $r = -2$. So the coordinates would be $(-2, 3\pi/2)$. But the answer at the back of the book is $(-2, \pi/2)$. Am I missing something? The book is "Precalculus: A Problems Oriented Approach" by David Cohen (6ed.)