# The Incircle and Excircles of a Triangle

Submitted by Isoscel on Sun, 12/30/2007 - 17:04.

Let ABC be a triangle. The incircle of ABC is the circle that is tangent to all its sides and it's in the interior of ABC. The three excircles of ABC are the three circles that are in the exterior of ABC and are tangent to the lines that contain the sides of ABC.