Editing Appendix/Ramblings/ToroidalCoordinates (section)

==Off-center Circle==
In what follows, it will be useful to recall the algebraic expression that defines a circle whose center is not positioned at the origin of a Cartesian coordinate system.  Specifically, consider a circle of radius, <math>~r_c</math>, whose center is located a distance <math>~x_0</math> along the plus-x axis and  a distance <math>~y_0</math> along the plus-y axis.  The equation for this circle is,
<div align="center">
<math>
~(x-x_0)^2 + (y-y_0)^2 = r_c^2 .
</math>
</div>