Answer:
Step-by-step explanation:
Let x = length of fenced side parallel to the side that borders the river
  y = length of each of the other two fenced sides Â
Then, x + 2y = 4500
<=> Â x = 4500- 2y
Â
Area = xy = y(4500-2y)
       = [tex]-2y^{2}[/tex] + 4500y
The graph of the area function is a parabola opening downward.
The maximum area occurs when y = -4500/[2(-2)] = 1125
                       x = 4500-2y = 2250
To maximize the area, the fenced side parallel to the pone be 2250 feet long, while each of the other two fenced sides should be 1125 feet long.