Creation of this applet was inspired by a [url=http://www.gogeometry.com/school-college/3/p1269-triangle-incircle-bisector-90-degree.htm]problem[/url] posted by [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url]. [br][br]You move any of the triangle's [b]LARGE WHITE VERTICES[/b] 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 the phenomenon dynamically illustrated here? [/b][/color]