Math Problem Statement

A carpenter is building a rectangular room with a fixed perimeter of 324 ft. What dimensions would yield the maximum area?

Solution

To find the dimensions that yield the maximum area for a rectangular room with a fixed perimeter, we can use some principles from optimization.

  1. Define the Problem: The perimeter PP of a rectangle with length LL and width WW is given by: P=2L+2WP = 2L + 2W Here, P=324P = 324 feet.

  2. Set Up the Equation: Using the given perimeter, we can rewrite this as: 2L+2W=3242L + 2W = 324 Dividing both sides by 2, we get: L+W=162L + W = 162 Now, solve for WW: W=162LW = 162 - L

  3. Express the Area: The area AA of the rectangle is: A=L×WA = L \times W Substitute W=162LW = 162 - L: A=L×(162L)A = L \times (162 - L) Expanding this gives: A=162LL2A = 162L - L^2

  4. Find the Maximum Area: To maximize the area, we can take the derivative of AA with respect to LL and set it to zero: dAdL=1622L=0\frac{dA}{dL} = 162 - 2L = 0 Solving for LL: 2L=1622L = 162 L=81L = 81 Substitute L=81L = 81 back into W=162LW = 162 - L: W=16281=81W = 162 - 81 = 81

  5. Conclusion: The dimensions that yield the maximum area are L=81L = 81 feet and W=81W = 81 feet, making the shape a square.

Answer:

  • Length (ft) = 81
  • Width (ft) = 81

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Additional Related Questions

  1. What would be the area of this room with these dimensions?
  2. Why does a square maximize the area for a given perimeter?
  3. How would the dimensions change if the perimeter were 400 feet instead?
  4. What would the length and width be if the room had to be twice as long as it is wide?
  5. How can this method be applied to maximize other shapes, like circles or triangles?

Tip: For rectangles with a fixed perimeter, the square configuration always provides the maximum area.

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Math Problem Analysis

Mathematical Concepts

Algebra
Optimization
Geometry

Formulas

Perimeter formula for a rectangle: P = 2L + 2W
Area of a rectangle: A = L * W

Theorems

The square configuration maximizes area for a fixed perimeter in a rectangle

Suitable Grade Level

Grades 9-10