Incircle
The incircle or inscribed circle of a
triangle ABC is the circle tangent to the three sides. The
center I of the incircle is called the incenter. The incenter is
the intersection of the three internal angle bisectors.
Excircle
An excircle or escribed circle of a
triangle ABC is an external circle, tangent to one of its sides
and tangent to the extensions of the other two. The center of an
excircle, called an excenter, is the intersection of the
internal bisector of one angle and the external bisectors of the
other two. Every triangle has three excenters D, E, F, each
tangent to one of the triangle's sides.
Tracenpoche
This page uses the
TracenPoche
dynamic geometry software and requires
Adobe Flash player 7 or higher.
TracenPoche is a project of Sesamath, an association of French
teachers of mathematics.
Dynamic Software
Dynamic Geometry: You can alter the figure above
dynamically in order to test and prove (or disproved)
conjectures and gain mathematical insight that is less
readily available with static drawings by hand.
Instruction to explore the
illustration above:

Animation. Click the red
button
to start/stop animation

Manipulate. Drag points A
and C to change the figure.

Step by Step construction.
Press P and click the left mouse
on any free area to show the
stepbystep bar and start the
construction:
Hide the stepbystep bar by
using again the combination P +
click left mouse.
