Answer:
Therefore the length and width of the playground are 15.5 feet and 12.9 feet respectively.
Step-by-step explanation:
Given that, a homeowner plans to enclose a 200 square foot rectangle playground.
Let the width of the playground be y and the length of the playground be x which is the side along the boundary.
The perimeter of the playground is = 2(length +width)
=2(x+y) foot
The material costs $1 per foot.
Therefore total cost to give boundary of the play ground
=$[ 2(x+y)×1]
=$[2(x+y)]
But the neighbor will play one third of the side x foot.
So the neighbor will play 
Now homeowner's total cost for the material is
![=\$[ 2(x+y)-\frac13x]](https://tex.z-dn.net/?f=%3D%5C%24%5B%202%28x%2By%29-%5Cfrac13x%5D)
![=\$[2x+2y-\frac13x]](https://tex.z-dn.net/?f=%3D%5C%24%5B2x%2B2y-%5Cfrac13x%5D)
![=\$[2y+x+x-\frac13x]](https://tex.z-dn.net/?f=%3D%5C%24%5B2y%2Bx%2Bx-%5Cfrac13x%5D)
![=\$[2y+x+\frac{3x-x}{3}]](https://tex.z-dn.net/?f=%3D%5C%24%5B2y%2Bx%2B%5Cfrac%7B3x-x%7D%7B3%7D%5D)
![=\$[2y+x+\frac{2}{3}x]](https://tex.z-dn.net/?f=%3D%5C%24%5B2y%2Bx%2B%5Cfrac%7B2%7D%7B3%7Dx%5D)
![=\$[2y+\frac53x]](https://tex.z-dn.net/?f=%3D%5C%24%5B2y%2B%5Cfrac53x%5D)
where C(x) is total cost of material in $.
Given that the area of the playground is 200.
We know that,
The area of a rectangle is =length×width
=xy square foot
∴xy=200

Putting the value of y in C(x)

The domain of C is
.

Differentiating with respect to x

Again differentiating with respect to x

To find the critical point set C'(x)=0





Therefore

Therefore at x= 15.5 , C(x) is minimum.
Putting the value of x in
we get

=12.9
Therefore the length and width of the playground are 15.5 feet and 12.9 feet respectively.