Definition:Excircle of Triangle/Excenter

Definition

 * Excircle-of-Triangle.png

The center of an excircle of a triangle is called an excenter of the triangle.

In the above diagram, $I_a$ is the excenter of $\triangle ABC$ $a$.

Also known as
In British English the spelling is usually excentre.

Some (usually older) sources refer to this as an ex-center or ex-centre.

The term ecenter or ecentre is can also be found, particularly in the U.S.