2-dim. pendulum: Which coordinates?

Question

I have a rather elementary question: I have a 2-dim pendulum and I do not know how I can descrive the coordinates.

In the 1-dim case one coordinates is enough_ the angle. But I do not know how it is here.

Answer 1

Perhaps the equation of a circle is what you are after for a 2 dimensional plane. Such as: $$ (x-a)^2 + (y-b)^2 = r^2 $$ Where r is the radius. The x and y are the coordinates of a cartesian plane. a and b are the coordinates by which the center of the circle is translated from the origin.
Here is a web page on circles you may find useful.
http://www.mathsisfun.com/algebra/circle-equations.html