Let x and y be the sides of the rectangle.
Then, set-up the equation for the total cost of the fence. To do so, let's use a $5 per foot fencing for the two sides "x" . And, $2 per foot fencing for the two sides "y".
So the equation is:
`4000 = 5(2x) + 2(2y)`
To simplify, divide both sides by its GCF which is 2.
`2000 =5x + 2y`
Then, solve for y.
Since we have to maximize the area of the rectangle, set-up the equation of area.
Note that `y= 1000-5/2x` . So,
Then, take the derivative of A.
Set A' equal to zero and solve for x.
`0 = 1000-5x`
`x = 200`
Substitute the value of x to `y = 1000-5/2x` .
`y=1000-5/2*200 = 1000-500=500`
Hence, the dimensions of the rectangular plot that would maximize its area, given the total cost of fencing, is `200 xx 500` ft.