I'm having some problems with finding, in radians, the argument of z and adding rotations of 180 to keep it in range. I know that I have to use:

and I know exact trigonometric ratios, and the ASTC in the polar plane. But I don't know where Arg Z is positive, and I don't know when to add or even just (pi = 180 in radians), to keep Arg Z in the range of . As you can see I am very confused, any help would be great.