Math Help - Shortest fence distance

Hi All,

Could someone please help me with what I am doing wrong with this optimization problem?...

Code:

A rancher wants to fence in an area of 2000000 
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?

My Work..

Code:

2000000 = ab ---> b = 2000000/a

L = 3a + 2b = 3a + 4000000/a

0 = L' = 3 - 4000000 / a^2

a = 3651.48ft

b = 4000000/ 3651.48 = 1095.45ft

Lmin = 3(3651.48) + 2(1095.45) =!?  13145.3ft

Any help is appreciated! I was following along with this example:
http://www.mathhelpforum.com/math-he...n-problem.html

-M

you put an extra zero in your calculator when you find out a.

recalculate a and its good

Haytham, Thanks for looking..

I did what you said and got 10392.3 for Lmin. However the program I am using is telling me it's the wrong answer. Could you or someone else confirm this?

Thank you,

-M

sorry didnt notice

b=2000000/a

you used b=4000000/a

Originally Posted by mant1s

Haytham, Thanks for looking..

I did what you said and got 10392.3 for Lmin. However the program I am using is telling me it's the wrong answer. Could you or someone else confirm this?

Thank you,

-M

Your answer for Lmin is wrong.

Do you get a = 1154.7 (correct to 1 decimal place)? If not, then you've made a mistake somwhere in your arithmetic.

yesss!

6928.2 = Lmin

Fantastic,

Yes I did get that for a (1154.7).

Thanks for taking a look.