Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/780090414112145409]problem[/url] posted by [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br][br]You can move the [b]3 WHITE VERTICES[/b] of the triangle anywhere you'd like. [br][b][color=#ff00ff]You can alter the size of the angle with pink vertex using the pink slider. [/color][/b][br][br][color=#38761d][b]How can we formally prove what is dynamically illustrated here? [/b][/color]