How do I know what quadrant u/2 is if u is in quadrant 3?

Question

I know how to use the half-angle formulas but I don't know how to find out which quadrant u/2 is in based off of what quadrant u is in.

Answer 1

 

Quadrant 3 is 180^o < θ < 270^o

If you divide the Q3 range by 2, you end up with  90^o < θ < 135^o

So if u is in Q3 then u/2 is in Q2.