> > using your formula, you always have to be aware what quadrant you are
> in.
> > If you get confused, go back to basics. Draw it out in a little sketch
> if
> > necessary. consider the point(-1,1) and the point (1,-1). the arctan of
> (-1)
> > is -45 in both cases, but the angle from the positive real axis is
> either
> > 135 or 225
>
> I always do this by dissolving everything into X and Y coordinates, then
> adding all those X and Y values up, then move back to Distance<Angle - I
> always get the same answers when I do that, and reliability is a GOOD
> thing <G>  Knowing where (-1,1) is, you can tell that 1.414<135 is the
> correct answer, and that 1.414<225 is not correct.  Do a fair amount of
> math, have seen some real doozies of math library bugs, have had to
> write my own more than once.
>
I agree totally. Hence my point about drawing a little sketch. It's
a great sanity check and helps you see what's happening (eg does
the answer make sense). I use the same approach of resolving into
X, Y if  I don't happen to have my calculator, which lets you enter
complex numbers (Re, Im) or (Distance,Angle) directly. I've always
hated blindly applying formulas, but after you know the
technique/theory, it is a legitimate time saver and still another
sanity check (although computing by hand can also be used as
a sanity check on the calculator)