Homework Help: calculus

Posted by Chris on Friday, December 16, 2011 at 5:54am.

Damon help again :) (last one I promise)
why is X along the road sqrt2/2?

] A rancher plans to set aside a rectangular region of one square kilometer for cattle and wishes to build a wooden fence to enclose the region. Since one side of the region will run along the road, the rancher decides to use a better quality wood for that side which costs three times as much as the wood for the other sides. What dimensions will minimize the cost of the fence?

x y = 1

c = 3 x + x + 2 y = 4 x + 2 y

c = 4 x + 2/x

dc/dx = 4 - 2/x^2
= 0 for minimum

4 = 2/x^2
x^2 = 1/2
x = 1/sqrt 2 = sqrt 2/2 along road
y = sqrt 2

calculus - drwls, Friday, December 16, 2011 at 6:13am
This question has already been answered by Damon
calculus - Chris, Friday, December 16, 2011 at 6:16am
Yes, I know, but I i had question about the answer... I'm math stupid :)
calculus - Damon, Friday, December 16, 2011 at 8:37am
The smaller of x or y will be the expensive fence along the road.

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