Math Problem Statement

If you have exactly 200 m of fencing to make either one square enclosure with two widths and two lengths or two separate square enclosures of any side you wish, what plan gives you the least area? The most?

Solution

To solve this, we’ll need to examine the two options: one square enclosure with two widths and two lengths, and two separate square enclosures, using the given 200 meters of fencing.

Option 1: One Square Enclosure

If you create one square enclosure with a perimeter of 200 meters, the perimeter equation for a square is:

P=4×side lengthP = 4 \times \text{side length}

Setting P=200P = 200, we get:

200=4×side length200 = 4 \times \text{side length}

Solving for the side length:

side length=2004=50m\text{side length} = \frac{200}{4} = 50 \, \text{m}

The area of a square is:

A=side length2=502=2500m2A = \text{side length}^2 = 50^2 = 2500 \, \text{m}^2

Option 2: Two Separate Square Enclosures

If you create two separate square enclosures, the total perimeter used is still 200 meters, but now the perimeter is split between the two squares. Let the side length of the first square be xx, and the side length of the second square be yy. The perimeter of each square is 4x4x and 4y4y, and the total perimeter equation is:

4x+4y=2004x + 4y = 200

Simplifying:

x+y=50x + y = 50

Now, the area of the two squares is:

A1=x2andA2=y2A_1 = x^2 \quad \text{and} \quad A_2 = y^2

The total area of both squares combined is:

Atotal=x2+y2A_{\text{total}} = x^2 + y^2

Since y=50xy = 50 - x, we substitute this into the area formula:

Atotal=x2+(50x)2A_{\text{total}} = x^2 + (50 - x)^2

Expanding:

Atotal=x2+2500100x+x2=2x2100x+2500A_{\text{total}} = x^2 + 2500 - 100x + x^2 = 2x^2 - 100x + 2500

This is a quadratic function, and to minimize or maximize the area, we can complete the square or use the vertex formula. The vertex formula for a quadratic equation ax2+bx+cax^2 + bx + c gives the value of xx at the vertex as:

x=b2ax = \frac{-b}{2a}

For our equation, a=2a = 2, b=100b = -100, and c=2500c = 2500, so:

x=(100)2(2)=1004=25x = \frac{-(-100)}{2(2)} = \frac{100}{4} = 25

Thus, the side length of the first square that minimizes the area is 25 meters, and the side length of the second square is y=5025=25y = 50 - 25 = 25 meters.

So, the minimum area occurs when both squares have side lengths of 25 meters, and the total area is:

Atotal=252+252=625+625=1250m2A_{\text{total}} = 25^2 + 25^2 = 625 + 625 = 1250 \, \text{m}^2

Conclusion:

  • The least area occurs when both squares have side lengths of 25 meters, with a total area of 1250 m².
  • The most area occurs when there is only one square enclosure with side length 50 meters, giving an area of 2500 m².

Recap:

  1. Most Area: 2500 m² (One square enclosure).
  2. Least Area: 1250 m² (Two separate square enclosures, each 25 meters in side length).

Would you like further clarification on the steps, or is there any other detail you'd like to explore? Here are a few more questions to expand on the topic:

  1. What would happen if the perimeter was different, say 100 meters, for each option?
  2. How would the area change if we used rectangular enclosures instead of squares?
  3. What is the geometric principle behind minimizing or maximizing the area with a fixed perimeter?
  4. How can calculus help in optimizing such enclosure problems?
  5. What is the impact of changing the shape of the enclosure (circle, for example) on the area?

Tip: In optimization problems like these, using the properties of quadratics can help find the maximum or minimum values quickly. The vertex formula is a key tool for these situations!

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Math Problem Analysis

Mathematical Concepts

Geometry
Optimization
Quadratic Functions
Perimeter
Area

Formulas

Perimeter of square: P = 4 × side length
Area of square: A = side length^2
Quadratic equation formula: ax^2 + bx + c

Theorems

Optimization of quadratic functions

Suitable Grade Level

Grades 9-12