Parallelograms

Parallelogram trivia:

Construct a rectangle with rigid sides top and bottom and rubber bands on the left and right sides, and set the top side in a track so it can slide left and right. As it slides, the rubber bands stretch and the four sides will enclose a parallelogram.

No matter how far you slide the top side in either direction, the area of the enclosed parallelogram will never change.
 
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