Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/882563596986744833]tweet[/url] from [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url]. [br][br][b]Feel free to move the BIG WHITE POINTS anywhere you'd like. [/b][br][b][color=#b4a7d6]You can adjust the size of the purple interior angle with the purple slider.[/color][/b][color=#674ea7][br][/color][br][b][color=#666666]How can we formally prove what this applet informally illustrates? [/color][/b] [br]