\begin{definition}[Definition:Angle of Intersection of Circles]
Let $\CC$ and $\CC'$ be circles whose centers are at $C$ and $C'$ respectively.
Let $\CC$ and $\CC'$ intersect at $A$ and $B$.
The '''angle of intersection''' of $\CC$ and $\CC'$ is the angle between the tangents at the point of intersection.
:540px
Of the two angles formed by the tangents, the angle taken is between:
:the half-line of one tangent that passes completely outside both circles
and:
:the half-line of the other tangent that passes through the interior of one circle.
\end{definition}