G.GCO.10 Rectangle Template
The applet below contains a quadrilateral that ALWAYS remains a rectangle. 
The purpose of this applet is to help you understand many of the geometric properties a rectangle has.  
Interact with this applet for a few minutes.  As you do, be sure to move points A, B, and D around! 
What do you notice about the relationships of opposite sides?
What do you notice about the 4 angles?
What do you notice about the lengths of the diagonals?
Do the diagonals always bisect each other?
Are the diagonals perpendicular?
Are the diagonals angle bisectors?