December 7th, 2017, 05:15 PM  #1 
Newbie Joined: Dec 2017 From: Ironton OH Posts: 2 Thanks: 0  Optimization Problem
Basically all I am struggling with is finding an equation for the function 𝒇(𝒙) giving the quantity that is to be maximized as a function of a variable. The rest of the problem is more complex but should be easy once I figure the first part out. The Problem: A park is to be in the shape of a rectangle, with a perimeter of 760 feet. The park is to be divided into 3 rectangular regions of equal size by two parallel walkways of equal width. Each of the 3 rectangular regions is to have an area of 9000 square feet. Design the park so that each walkway is as wide as possible. 
December 7th, 2017, 06:09 PM  #2 
Senior Member Joined: Sep 2015 From: USA Posts: 1,691 Thanks: 859 
Let $W$ be the width of the park and $\delta$ the width of a pathway. The park will have perimeter $P = 760 = \dfrac{54000}{W} + 4 \delta + 2W$ $\delta = \dfrac{760  2W\frac{54000}{W}}{4}$ $\dfrac{d\delta}{dW} = \dfrac 1 2 +\dfrac{13500}{w^2}$ $\dfrac{d\delta}{dW} = 0 \Rightarrow \dfrac{13500}{w^2}= \dfrac 1 2$ $w^2 = 27000$ $w = 30\sqrt{30}$ $\delta = 19030 \sqrt{30} \approx 25.68$ 
December 7th, 2017, 07:16 PM  #3 
Senior Member Joined: Sep 2015 From: USA Posts: 1,691 Thanks: 859 
oops.. all $w's$ should be $W's$

December 7th, 2017, 07:47 PM  #4 
Math Team Joined: Jul 2011 From: Texas Posts: 2,691 Thanks: 1350  
December 8th, 2017, 10:23 PM  #5  
Newbie Joined: Dec 2017 From: Ironton OH Posts: 2 Thanks: 0  Quote:
 

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