Three of the sides will require fencing and the fourth wall already exists. If the farmer has 144 feet of fencing what is the largest area the farmer can enclose ?

A farmer is building a fence to enclose a rectangular area against an existing wall. Three of the sides will require fencing and the fourth wall already exists. If the farmer has 144 feet of fencing, what is the largest area the farmer can enclose?

Answer:

A_largest = 2592 ft²

Step-by-step explanation:

Let the width which is going to be perpendicular to the already existing fourth wall be denoted by y. Since there will be 2, it means total width = 2y.

Since the farmer has 144 ft of fencing and the total width is 2y,it means that the length of the fence will be expressed as;

Length = 144 - 2y

Area of rectangular fencing is;

A = y(144 - 2y)

A = 144y - 2y²

To find the largest area, we will find the first derivative and the equate to 0 after which we plug the value of y back into the area equation to get it.

dA/dy = 144 - 4y

At dA/dy = 0;

144 - 4y = 0

y = 144/4

y = 36 ft

Thus, largest area is;

A_largest = 144(36) - 2(36)²

A_largest = 2592 ft²

eudora eudora · Answer 2 · 2021-11-16T19:36:33+01:00

The largest area the farmer can enclose with the fence with him will be 2592 square feet.

Let the length of the field = [tex]x[/tex] feet

And the width of the field = [tex]y[/tex] feet

Therefore, area of the rectangular field = Length × Width

A = [tex]x\times y[/tex] square feet

Since, length of the fence = 144 feet

And the farmer has to enclose three sides of the rectangle as shown in the figure attached.

Therefore, length of the fence = length + 2(width)

= [tex](x+2y)[/tex] feet

Hence, [tex](x+2y)=144[/tex]

[tex]x=144-2y[/tex]

By substituting the value of 'x' in the expression for the area of the rectangular field.

[tex]A=(144-2y)y[/tex]

[tex]A=-2y^2+144y[/tex]

Find the derivative of the expression with respect to [tex]y[/tex],

[tex]A'=-4y+144[/tex]

Now equate it to zero to get the value of y,

[tex]A'=-4y+144=0[/tex]

[tex]y=36[/tex]

Now substitute the value of 'y' in the expression of area to get the maximum area enclosed.

[tex]A=-2(36)^2+144(36)[/tex]

[tex]=-2592+5184[/tex]

[tex]=2592[/tex] square feet

Therefore, maximum area the farmer can enclose with the 144 feet of fencing will be 2592 square feet.

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