Exterior Angle of Triangle with Geo and Desmos

In Accelerated Geometry, I introduced the students to the Exterior Angle of a Triangle Theorem.  I did not straight out tell them the theorem.  I wanted them to "discover" it using the Desmos activity.  However, the first question was what is the theorem.  Some thought it was all the exterior angles add to 360 degrees - true.  Some thought it was the exterior angle of a triangle is greater than each far angle.  True, too.  So, I drew a picture on the board and we discovered the connection that way, then we dove into practicing with Desmos.  I loved seeing them sketch their pictures: