A rancher needs to enclose two adjacent rectangular​ corrals, one for cattle and one for sheep. if the river forms one side of the corrals and 180 yd of fencing is​ available, find the largest total area that can be enclosed.

Respuesta :

Refer to the diagram shown below.

x = the width of each rectangular fence
y = the length of each rectangular fence

The amount of fencing available is 180 yards, therefore
2x + 2y = 180
x + y = 90               (1)

The total fenced area is
A = 2xy                 (2)

From (1), obtain
y = 90 -x               (3)
Substitute (3) into (2).
A = 2x(90 - x) = 180x - 2x²

To maximize A,
A'(x) = 180 - 4x = 0   => x = 180/4 = 45 yds
y = 90 -x = 45 yds

The largest total enclosed area is
A = 2*x*y = 2*45² = 4050 yd²

Answer: 4050 yd²
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