# Need help with Trig/angle question

1. Jan 28, 2007

### jkh4

For example: if i have a point (1, -1) in the forth quadrant of the xy plane. How do you convert it to angle = [7(pie)/2]+2n(pie) format? i just forget how to do that part. Also, what if the answer for tan-1(angle) is not a whole #, ex: 53.1, then how do you do the conversion? Thank you.

Last edited: Jan 28, 2007
2. Jan 30, 2007

### sphoenixee

To convert from rectangular (x,y) to polar (r,theta):
r=Sqrt[x^2+y^2]
theta=arctan(y/x), after which you must consider the given quadrant

See wikipedia: http://en.wikipedia.org/wiki/Polar_...rting_between_polar_and_Cartesian_coordinates

If you get an irrational answer in degree form, it's probably going to be irrational in radians form as well, e.g. tan-1[4/3]~53.130deg~.927r. in this case, there's no neat a*Pi+2nPi form, where a is rational and n is integer.

sphoenixee