Creation of this applet was inspired by a [url=http://www.gogeometry.com/school-college/3/p1220-scalene-equilateral-triangles-midpoint-class.htm]problem[/url] posted by [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br][br]You can change the size of the [b][color=#9900ff]interior angle with purple vertex[/color][/b] by using the [b][color=#9900ff]purple slider. [/color][/b] [br]Feel free to place any of the triangle's vertices where you'd like at any time. [br][color=#ff00ff][b][br]How can we formally prove what is dynamically illustrated here?[/b][/color]