Creation of this applet was inspired by [url=https://twitter.com/Cshearer41/status/1205759305783431168?s=20]this problem[/url] posted by [url=https://twitter.com/Cshearer41]Catriona Shearer[/url]. [br][br]What is the measure of the [b][color=#ff00ff]angle[/color][/b] that appears? [br]What is the measure of the angle labeled with a [b]?[/b] ? [br][br]How can we formally prove what is dynamically illustrated here?