Shearer Action 6!

Creation of this resource was inspired by this tweet from Catriona Shearer. Below, we have 2 squares with a common vertex. You can move any of the LARGE POINTS anywhere you'd like AT ANY TIME. Questions: 1) What is the measure of the (soon-to-appear) pink angle? 2) How can we explain why the measure of the pink angle at the end (with green vertex) never changes?

Quick (Silent) Demo