Khan Academy
Khan Academy: Find Angles in Triangles
Find missing angle measures using the properties of triangles. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video, or receive hints.
Texas Instruments
Texas Instruments: Properties of the Centers of a Triangle
Students investigate the sum of the measures of the interior angles of a triangle. This activity explores interior angles, and their relationship with the exterior angles of a triangle [Requires Adobe Reader.]