What geometry vocabulary term (definition) and what theorems are dynamically demonstrated in the applet below? (Feel free to move this quadrilateral's white vertices anywhere you'd like!)
[color=#000000][b]Definition of a Rectangle:[/b][/color][br]A rectangle is a quadrilateral with [b]4 right angles[/b]. [br][br][b][color=#000000]Theorems:[/color][/b][br]The [color=#1e84cc][b]diagonals[/b][/color] of a rectangle [color=#1e84cc][b]are congruent[/b][/color]. [br]Each [color=#1e84cc][b]diagonal [/b][/color]of a rectangle splits a [b]right angle[/b] into 2 complementary angles. The measures of these two angles are the same two angle measures into which each of the rectangle's other 3 right angles are split. [br][br]Note that the [color=#000000][b]Isosceles Triangle Theorem[/b][/color] is also manifested here: If [color=#1e84cc][b]two sides[/b][/color] of a triangle [color=#1e84cc][b]are congruent[/b][/color], then the [color=#38761d][b]angles[/b][/color] (or [color=#ff00ff][b]angles[/b][/color]) opposite [color=#1e84cc][b]those sides[/b][/color] are congruent.