You can specify the position of a point in a Cartesian plane by specifying its distance, R, from the origin, and the angle to the positive x-axis in a counterclockwise direction, the angle α.
If you right-click on a point in the algebra view you can choose to show the polar coordinates instead of the Cartesian coordinates. GeoGebra writes polar coordinates by using a semi-colon instead if a comma.
If you want to enter a point using polar coordinates in the input bar, use a semi-colon.
The degree-symbol can be found in the symbol-menu beside the input bar, it can also be written Ctrl+o.
Epitrochoids using polar coordinates
As an example of how to use polar coordinates, the model of the sun, earth, and moon will be used. See GeoGebra Tutorial - Epicycles.
Input a slider
R for the radius of the earth's orbit around the sun, and a slider
r for the
radius of the moon's orbit around the earth. Input a slider
α to denote the angle and a
months to denote the number of months in a year.
A denote the earth, and
B the moon . The coordinates of the points can be entered in
polar form as:
Put a trace on
B. It is also possible to show the locus of
on the Locus tool, then on
B, then on the slider
by Malin Christersson under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 Sweden License