[color=#000000]The applet below dynamically illustrates the [url=https://en.wikipedia.org/wiki/Japanese_theorem_for_cyclic_quadrilaterals]Japanese Theorem for Cyclic Quadrilaterals[/url]. [br]How can you formally prove what is informally illustrated here?[br][/color][br][color=#000000]Does it look like the sides of the rectangle are curved? (Believe it or not, they aren't!) [/color]