What phenomenon is dynamically being illustrated in the applet below? How would you describe in words? How can we formally prove this true?
For more information, see this [url=http://www.gogeometry.com/problem/p404_equilateral_triangle_congruence_60_degrees_area.htm]post[/url] from Antonio Gutierrez ([url=http://www.gogeometry.com/]GoGeometry[/url]).