This is probably a basic concept that I just never really grasped...now I'm in Calc III and it's biting me in the butt.

I need to find theta = arctan(-1/2)

I typed it into my calculator to receive the answer-.464 radians

But calculators are limited when it comes to solving trig, and as I understand there are other answers other than what I received. How do I go about finding the other answer(s)?