Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/784807966214123520]tweet[/url] from [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry.) . [br][br]Feel free to move the [b][color=#1e84cc]2 blue points[/color][/b] and/or [b]2 white points[/b] anywhere you'd like at any time. [br][br][b][color=#ff00ff]How can we formally prove what this applet dynamically illustrates? [/color][/b]