Move the slider to change the width and determine which rectangle has the greatest area.

What is the length and width of the rectangle with maximum area?

Suppose this rectangle is a cattle pen with perimeter 40 yards. If each cow needs 1 square yard of space, what is the maximum amount of cattle you can fit in this pen?

Suppose you have a rectangle with fixed perimeter p. What is the length and width of the rectangle with maximum area? What is the maximum area?