What (not-often-seen) theorem is dynamically being illustrated below? [br](Feel free to move the triangle's vertices and the [b][color=#1e84cc]BIG BLUE POINT[/color][/b] wherever you'd like.)
Details of this theorem are specifically described in this [url=https://twitter.com/gogeometry/status/816420809560494081]tweet[/url] from [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url].