SOLUTION: A farmer decides to enclose a rectangular​ garden, using the side of a barn as one side of the rectangle. What is the maximum area that the farmer can enclose with 60 ft of&#

Algebra ->  Length-and-distance -> SOLUTION: A farmer decides to enclose a rectangular​ garden, using the side of a barn as one side of the rectangle. What is the maximum area that the farmer can enclose with 60 ft of&#      Log On


   



Question 1058410: A farmer decides to enclose a rectangular​ garden, using the side of a barn as one side of the rectangle. What is the maximum area that the farmer can enclose with 60 ft of​ fence? What should the dimensions of the garden be to give this​ area?
And,
Total profit P is the difference between total revenue R and total cost C. Given the following​ total-revenue and​ total-cost functions, find the total​ profit, the maximum value of the total​ profit, and the value of x at which it occurs.
R(x)=1300x-(x-squared)
C(x)=3100+20x

Found 2 solutions by ikleyn, josmiceli:
Answer by ikleyn(52756) About Me  (Show Source):
You can put this solution on YOUR website!
.
See the lesson
    - A farmer planning to fence a rectangular area along the river to enclose the maximal area
in this site.

Very similar problem was solved there for you. It is precisely your case, your prototype, your sample.
Read it attentively and then solve your problem by substituting your data.

Also, you have this free of charge online textbook in ALGEBRA-I in this site
    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.

The referred lesson is the part of this textbook under the topic "Finding minimum/maximum of quadratic functions".

The other lessons under this topic are
    - HOW TO complete the square to find the minimum/maximum of a quadratic function
    - Briefly on finding the minimum/maximum of a quadratic function
    - HOW TO complete the square to find the vertex of a parabola
    - Briefly on finding the vertex of a parabola
    - A rectangle with a given perimeter which has the maximal area is a square
    - A farmer planning to fence a rectangular garden to enclose the maximal area
    - A rancher planning to fence two adjacent rectangular corrals to enclose the maximal area


Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +L+ = the length of the rectangle
Let +W+ = the width of the rectangle
--------------------------------------
Use formula for perimeter of a rectangle
+2L+%2B+2W+=+60+
+2L+=+60+-+2W+
+L+=+30+-+W+
--------------------
Let +A+ = the area of the rectangle
+A+=+W%2AL+
+A+=+W%2A%28+30+-+W+%29+
+A+=+-W%5E2+%2B+30W+
-----------------------
This is a parabola. To find the peak, use the
formula +W%5Bmax%5D+=+-b%2F%282a%29+, where the
form is:
+A+=+a%2AW%5E2+%2B+b%2AW+%2B+c+ ( +c=0+ )
+W%5Bmax%5D+=+-30%2F%282%2A%28-1%29+%29+
+W%5Bmax%5D+=+15+
-----------------------
Plug this result back into equation
+A%5Bmax%5D+=+-15%5E2+%2B+30%2A15+
+A%5Bmax%5D+=+-225+%2B+450+
+A%5Bmax%5D+=+225+ ft2
--------------------------------
+A+=+W%2AL+
+225+=+15%2AL+
+L+=+15+ ft
The maximum area is a 15 x 15 square
--------------------------------------------
+P%28x%29++=+R%28x%29+-+C%28x%29+
+P%28x%29+=+1300x+-x%5E2+-+3100+-+20x+
-----------------------------------
+P%28x%29+=+-x%5E2+%2B+1280x+-+3100+
This is the expression for profit
-----------------------------------
Use formula for +x%5Bmax%5D+
+x%5Bmax%5D+=+-b%2F%282a%29+
+a+=+-1+
+b+=+1280+
+x%5Bmax%5D+=+-1280%2F%282%28-1%29%29+
+x%5Bmax%5D+=+640+
Plug this value back into equation
+P%5Bmax%5D+=+-640%5E2+%2B+1280%2A640+-+3100+
+P%5Bmax%5D+=+-409600+%2B+819200+-+3100+
+P%5Bmax%5D+=+406500+
-----------------------------
Here's the plot of the profit:
+graph%28+600%2C+400%2C+-160%2C+1600%2C+-45000%2C+450000%2C+-x%5E2+%2B+1280x+-+3100+%29+
My numbers look close