Parallelogram + 2 Equilateral Triangles: How to Prove?
Creation of this applet was inspired by a problem presented by Roberto Soto & Armando Martinez-Cruz (California State University, Fullerton) at their NCTM talk, "GeoGebra + GoFormative for Problem Solving, Problem Posing, and Assessment" (April 27, 2018).
You can move any of the LARGE WHITE POINTS anywhere you'd like AT ANY TIME.
You can also control the size of the (soon-to-appear) angle with pink vertex by using the pink slider.
How would you describe what you seen in your own words?
How can we formally prove what is dynamically illustrated here?