In converting from cartesian to polar, why does Arctan(-1) approximate to -pi/4? I'm studying Calculus but I forgot to do this part. The formula for getting theta is Arctan(y/x), and I am solving a problem where x=2 and y=-2. My notes shows that Arctan(-1), with some adjustments, approximates to -pi/4. How so? I need to know how to get the theta equivalent of it so I can graph it in a unit circle.

Since $\sin(-\pi/4)=-\sqrt{2}/2$ and $\cos(-\pi/4)=\sqrt{2}/2$, we have $\tan(-\pi/4)=-1$.
Michael
