GoGeometry Action 82!

Creation of this applet was inspired by a couple of [color=#0000ff]tweets[/color] from [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br]References: [url=https://twitter.com/gogeometry/status/888057017931378689]This tweet[/url] & [url=https://twitter.com/gogeometry/status/887798457968316416]this tweet[/url]. [br][br][b][color=#ff00ff]You can control the size of the angle with pink vertex using the pink slider. [/color][/b][br]Feel free to move the vertices of the triangle anywhere you'd like. [br][br][color=#9900ff][b]How can we formally prove the phenomena informally illustrated here? [/b][/color]

Information: GoGeometry Action 82!