How to get angle from -120-35i?

Question

anonymous · Answer

I thought it was atan(35/120) but why is the answer -163.73? Seems like they subtract atan(-35/-12) by 180..  Any rules I am not aware of it

mathstudent55 · Answer

This is a third quadrant angle.
Since the inverse tangent of a positive number gives you the reference angle in the first quadrant, you must then calculate what that angle will be in the third quadrant by either adding or subtracting 180 degrees.

anonymous · Answer

But then should that not be +180?

mathstudent55 · Answer

What do you get for atan(35/120)?

anonymous · Answer

16.26

anonymous · Answer

Do you know why we're looking for this angle oppose to the other one?

anonymous · Answer

|dw:1361074794122:dw|

mathstudent55 · Answer

|dw:1361074770992:dw|
Angle alph is the reference angle and it does measure 16.26... degrees.

anonymous · Answer

ahh I'm kind of confused

anonymous · Answer

Don't get why they subtracted 180