Shearer Action 2! (Semicircular Angle Problem)

Creation of this resource was inspired by [url=https://twitter.com/Cshearer41/status/1029760468406157313]this tweet[/url] from [url=https://twitter.com/Cshearer41]Catriona Shearer[/url]. [br][br]You can move any of the [b]3 LARGE POINTS[/b] anywhere you'd like at any time. [br][br][b][color=#ff00ff]What is the measure of the (soon-to-appear) pink angle? [/color][/b][br][br][color=#1e84cc][b]How can we formally prove this is always the case? [/b][/color]
Quick (Silent) Demo

Informaţie: Shearer Action 2! (Semicircular Angle Problem)