Carnot Action! = GoGeometry Action 27!

The following applet dynamically illustrates [b]Carnot's Theorem [/b]for the case of an [b][color=#bf9000]OBTUSE TRIANGLE.[/color][/b] [br][b][color=#ff00ff](The pink slider controls the measure of the obtuse angle with pink vertex.) [/color] [br][br][/b]Without looking it up on another tab in your internet browser, how would you put Carnot's Theorem into words?[br][br][b][color=#0000ff]How can you formally prove what this applet informally illustrates? [br][br][/color][/b](A huge thank you to [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url], whose [url=https://twitter.com/gogeometry/status/853627650212024320]tweet[/url] inspired the creation of this applet.)
Quick (Silent) Demo

Information: Carnot Action! = GoGeometry Action 27!