Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/836938468253138944]tweet[/url] posted by [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url]. [br][br]Feel free to move the triangle's 3 vertices anywhere you'd like at any time. [br][br][b][color=#0000ff]How can you formally prove what this applet informally illustrates? [/color][/b]