Question

Esme wants to make a rectangular pen for her chickens. She has 140 feet of fencing available to use. She wants to put the pen against the side of her barn. In other words, one side of the pen does not need fencing. Determine the maximum possible area she can create.

Answer 1

2450 square feet

Explanation:

We can first draw a rectangle with one side labeled Esme's wall. Then on one of the sides perpendicular to the "wall", we can assign a variable "x" for its length. The opposite of that side must have the same length "x". The unlabeled side that is opposite to the wall must have a length of "140-2x" because only 140 feet of fencing is available.

The area of a rectangle is equal to its length times its width, so the area of Esme's pen must equal "x" times "140-2x". If we graph this on a graphing calculator, we get a concave-down parabola. Since the input (x-axis) of this graph is the length of "x" and the output (y-axis) is the area Esme's pen, the highest y-value (which is the y-value of the vertex) will be the highest area that she can create. The vertex of this graph is (35, 2450), so the maximum area is 2450 square feet.

The non-calculator method involves expanding the expression "x(140-2x)" and finding the vertex through converting the expression to vertex form. (but... I'm too lazy to write out the vertex form for this expression so sorry no work here)