[color=#000000]This sketch works because AB stays constant (13.31).[/color]When point C is dragged, the length and width of theshaded purple shape change with it correspondingly.The circle creates a segment EF that is congruent to AC.The midpoint D defines the the other two segments[color=#000000]([/color]CD and BD), [color=#000000]ensuring that they remain congruent [/color]as the shapes area changes. [br]