A rancher has 600 feet of fencing to put around a rectangular field and then subdivide the field into 2 identical smaller rectangular plots by placing a fence parallel to one of the field's shorter sides. Find the dimensions that maximize the enclosed area. Write your answers as fractions reduced to lowest terms

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Answer:

Step-by-step explanation:

There's the two widths, x.

There's the four lengths, y.

4y+2x=600

Also, A=xy.

x=300-2y

A=y*(300-2y)

dA/dy=0= y*(-2)+(300-2y)

-2y-2y+300=0

y=300/4=150/2=75

x=300-2y=300-150=150

Then the long side is 150ft, the short side is 75ft.

Check to make sure that the sum of the lengths is 600: 300+300=600

And the maximum area is 150*75 ft2

Maximizing the area of a field, means we want to get the highest possible area of the field.

The dimensions that maximize the area are: 75ft by 150ft

The given parameters are:

[tex]A = 600[/tex] --- the area of the field

The area of the field is:

[tex]A =x \times y[/tex] -- area of rectangle

When the field is divided into 2 smaller plots, the area of the field becomes:

[tex]A = 2x + 4y[/tex]

Substitute 600 for A in [tex]A = 600[/tex]

[tex]2x + 4y = 600[/tex]

Divide through by 2

[tex]x + 2y = 300[/tex]

Make x the subject

[tex]x = 300 - 2y[/tex]

Substitute [tex]x = 300 - 2y[/tex] in [tex]A =x \times y[/tex]

[tex]A=(300 - 2y) \times y[/tex]

Open bracket

[tex]A=300y - 2y^2[/tex]

Differentiate with respect to y

[tex]A'=300 - 4y[/tex]

Set to 0

[tex]300 - 4y=0[/tex]

Collect like terms

[tex]4y = 300[/tex]

Divide both sides by 4

[tex]y = 75[/tex]

Recall that: [tex]x = 300 - 2y[/tex]

[tex]x =300 - 2 \times 75[/tex]

[tex]x = 150[/tex]

Hence, the dimensions that maximize the area are: 75ft by 150ft

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