Triangle Incenter

This applet demonstrates how the centriod of a triangle is constructed.

[b]Move[/b] points [color=#1551b5]A, B[/color] and [color=#1551b5]C[/color] and notice what happens to the triangle. 1. What are the red lines on the triangle? How do you know? 2. What is point D called? 3. Constructing a circle inside triangle ABC is called what? 4. What are the radii of the circle? Do they ever change?