Basic trig question for physics

[laminar]

I have to calculate the phase constant for a mass and spring system for simple harmonic motion. If I find that phi equals the arctan of some negative over another negative number, do I have to add pi to the answer for it to be in quadrant III?

I know this is more of a precalculus question but I don't know if the rules are different for physics.

 

[courtrigrad]

yes, you have to add $$\pi$$.