Can you please show step by step how to approach this answer and can you breifly
ID: 2891389 • Letter: C
Question
Can you please show step by step how to approach this answer and can you breifly explain what you are doing thanks!
Solve the problems below that pertain to constructing a fence (a) A farmer wishes to enclose 13,456 ft2 of land along a river by three sides of fence (the river forms the fourth side of the rectangular area). Find the dimensions which require the minimum length of fence. Let x be the length of the sides perpendicular to the river, and y the length of the parallel side.) (b) How does the answer from part (a) change if the fence is divided into three equal sections by two additional lengths of fence parallel to the river. (c) Suppose that, in the situation from part (b), the farmer is not limited by the area of the fence, but instead has only 1000 feet of fence available. What is the largest area he can enclose? ft2Explanation / Answer
Solution:
(a)
S = 2x + y........(i)
A = xy = 13456 .............(ii)
From (i) and (ii);
S = 2x +13456/x
dS/dx = 2-13456/x^2 =0
2x^2 = 13456
x^2 =13456/2 = 6728
x = 82.02 ft
y =13456/82.02 =164.06 ft
(b)
S = 2x + 3y........(i)
A = xy = 13456 .............(ii)
From (i) and (ii);
S = 2x + 3 * 13456/x
dS/dx = 2 - 40368/x^2 =0
2x^2 = 40368
x^2 = 40368/2 = 20184
x = 142.07 ft
y =13456/142.07= 94.71 ft
(c)
1000 ft = 2x + 3y .....(1)
A = xy ......(2)
From (i) and (ii);
1000 = 2x + 3(A/x)
1000x = 2x^2 + 3A
2x^2 - 1000x + 3A = 0
4x - 1000 + 3dA/dx = 0
dA/dx = (1000 - 4x)/3
dA/dx = 0;
1000 - 4x = 0 => x = 250ft
from ....(1)
1000 ft = 2*250 + 3y
=> 3y = 500 => y = 500/3 = 166.67 ft
So maximum Area = 250 ft * 166.67 ft = 41667.50 ft^2