Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/931639060191379456]tweet[/url] from [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br][br][b]You can move the 3 LARGE WHITE VERTICES of the triangle anywhere you'd like.[/b][br][b][color=#1e84cc]You can also alter the size of the blue angle using the blue slider. [/color][/b][br][b][color=#ff00ff][br]How can we formally prove what is dynamically illustrated here?[/color][/b] [br][br]