convert the rectangular to polar (-2,3)
We know that
$\displaystyle x = r \, cos \theta$
$\displaystyle y = r \, sin \theta$
So, upon inverting this:
$\displaystyle r = \sqrt{x^2 + y^2}$
$\displaystyle \theta = atn \left ( \frac{y}{\sqrt{x^2+y^2}} \right )$
(Which you can likely look up. I can never seem to remember the equations, so I derive them.)
Anyways:
$\displaystyle r = \sqrt{(-2)^2 + 3^2} = \sqrt{4+9} = \sqrt{13}$
$\displaystyle \theta = atn \left ( \frac{3}{\sqrt{(-2)^2+3^2}} \right ) = atn \left ( \frac{3}{\sqrt{13}} \right )$ (radians)
Off the top of my head I don't believe that the angle simplifies.
-Dan