\begin{definition}[Definition:Polar of Point/Circle]
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:
:$x x_0 + y y_0 = r^2$
\end{definition}