By using the distance formula for the polar form of points:[br][math]d^2=r^2+s^2-2rs\cos\left(\alpha-\beta\right)[/math][br]we can come up with an equation for a circle.[br][br]The circle is the the set of all random points, [math]\left(r,\theta\right)[/math], that are [math]d[/math] units away from a fixed point [math]\left(r_0,\theta_0\right)[/math].[br]This yields:[br][math]d^2=r^2+r_0^2-2rr_0\cos\left(\theta-\theta_0\right)[/math][br][br]Adjust the sliders for [math]r_0[/math], [math]\theta_0[/math], and [math]d[/math] to see how the graph and equation for the circle change.