GoGeometry Action 174!

Creation of this resource was inspired by a [url=http://www.gogeometry.com/school-college/5/p1425-two-squares-concurrent-lines.htm]problem[/url] posted by [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br][br]You can move any of the [b]LARGE WHITE POINTS[/b] anywhere you'd like [b]AT ANY TIME[/b]. [br][br][br][b][color=#ff00ff]How would you describe the phenomenon you see here? [br][br]How can we formally prove this true? [/color][/b]
Quick (Silent) Demo

Information: GoGeometry Action 174!