Definition:Polar of Point/Circle

Definition
Let $\CC$ be a circle whose radius is $r$ and whose center is at the origin of a Cartesian plane.

Let $P = \tuple {x_0, y_0}$ be an arbitrary point in the Cartesian plane.

The polar of $P$ with respect to $\CC$ is the straight line whose equation is given by:


 * $x x_0 + y y_0 = r^2$

Also see

 * Definition:Chord of Contact on Circle: when $P$ is specifically outside $\CC$