Calculus
posted by Z32 .
A rancher wants to fence in an area of 5189400 square feet in a rectangular field and then divide it in half with a fence down the middle parallel to one side. What is the shortest length of fence that the rancher can use?

Let x and y be the two side lengths of the full rectangle. The length x will be divided in two. The total lengths of fence needed will be
L = 2x + 3y.
You know that x y = 5,189,400 ft^2
dL/dx = d/dx (2x + 3*5,189,400/x)
= 2  15,568,200/x^2 = 0 at minimum L
x^2 = 7,784,100
x = 2790 ft y = 1860
Quantity of fence needed = 2x + 3y = ?