Question 43941
polar coordinates are written in the from (r, theta) were r is the radius and theta is the anti-clockwise angle for the positive x-axis.
The radius is easy to calculate:
{{{r=sqrt(x^2+y^2)}}}
and theta can be found using:
{{{theta=atan(y/x)}}}
where atan is the inverse of the tan function.

If x=0, the angle is either 90 or 180 degrees. If y>0 and x=0, theta is 90 degrees.
If y<0 and x=0, theta is 180 degrees.

In polar form, (0,-3) is (3,180) where theta is measured in degrees, or 
if the angle is in radians: r=3, theta=0.75*pi (3, 0.75pi)

I hope this helps. If you have any other problems, please dont hesitate to contact me at adam.chapman@student.manchester.ac.uk