Math Problem Statement

A gardener with 100 m of available fencing wishes to enclose a rectangular field and then divide it into two plots with a fence parallel to one of the sides. What is the largest area that can be enclosed?

Solution

To maximize the area, let’s break down the problem:

  1. Define Variables:

    • Let xx be the width of the entire rectangular field (the shorter side).
    • Let yy be the length of the field (the longer side parallel to the dividing fence).
  2. Fence Constraints:

    • The field has 3 sections of width xx: the two vertical sides and one internal dividing fence.
    • The field has 2 sections of length yy: the top and bottom.
    • Since the total fencing is 100 meters, we can write the constraint as: 3x+2y=1003x + 2y = 100
  3. Area of the Field:

    • The area AA of the rectangular field is given by: A=xyA = x \cdot y
  4. Express yy in Terms of xx:

    • From the fence constraint equation 3x+2y=1003x + 2y = 100, solve for yy: y=1003x2y = \frac{100 - 3x}{2}
  5. Substitute yy into the Area Formula:

    • Substitute y=1003x2y = \frac{100 - 3x}{2} into A=xyA = x \cdot y: A=x1003x2A = x \cdot \frac{100 - 3x}{2} Simplifying, we get: A=100x3x22A = \frac{100x - 3x^2}{2} A=50x3x22A = 50x - \frac{3x^2}{2}
  6. Maximize the Area AA:

    • To find the maximum area, take the derivative of AA with respect to xx and set it to zero: dAdx=503x=0\frac{dA}{dx} = 50 - 3x = 0 Solving for xx: x=503x = \frac{50}{3}
  7. Find yy Using x=503x = \frac{50}{3}:

    • Substitute x=503x = \frac{50}{3} back into the equation for yy: y=1003(503)2=100502=25y = \frac{100 - 3\left(\frac{50}{3}\right)}{2} = \frac{100 - 50}{2} = 25
  8. Calculate the Maximum Area:

    • Substitute x=503x = \frac{50}{3} and y=25y = 25 into the area formula A=xyA = x \cdot y: A=503×25=12503416.67 m2A = \frac{50}{3} \times 25 = \frac{1250}{3} \approx 416.67 \text{ m}^2

Final Answer:

A=12503m2A = \frac{1250}{3} \, \text{m}^2

Would you like further clarification on any step?


  1. How do we solve problems involving optimization and constraints?
  2. Why do we take derivatives to find maximum or minimum values?
  3. How does fencing length affect the shape and area of enclosures?
  4. What happens if we add more sections within the field?
  5. How would the answer change with different total fence lengths?

Tip: In optimization problems, always start by expressing the area (or volume) in terms of a single variable using constraints, then maximize or minimize it using calculus.

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Math Problem Analysis

Mathematical Concepts

Optimization
Calculus
Algebra

Formulas

Area of a rectangle: A = x * y
Fence constraint equation: 3x + 2y = 100
Substitution method to express y in terms of x: y = (100 - 3x) / 2
Optimization using derivatives

Theorems

Maximization of a function using derivatives

Suitable Grade Level

Grades 11-12