The sum of a triangle's angles is 180 degrees

Author:
qhaughey
This Geogebra sketch is an explanation of how to prove that the sum of a triangle's angles is 180 degrees. It was created by Quinn Haughey at Animas High School.
I would like you to move the points on the triangle around and see what kind of angle combinations you can come up with. Can you make an equilateral triangle?