Math Problem Statement

Among all rectangles that have a perimeter of 188, find the dimensions of the one whose area is largest. Write your answers as fractions reduced to lowest terms.

Solution

The problem is asking us to find the dimensions of a rectangle with the largest area, given that its perimeter is 188. Let's go step by step.

Given:

  • Perimeter P=188P = 188
  • We need to maximize the area of the rectangle.

Step 1: Relationship between dimensions and perimeter

Let the dimensions of the rectangle be ll (length) and ww (width). The perimeter of a rectangle is given by: P=2l+2wP = 2l + 2w Substitute P=188P = 188: 188=2l+2w188 = 2l + 2w Dividing both sides by 2: 94=l+w94 = l + w Thus, we have: l=94wl = 94 - w

Step 2: Area of the rectangle

The area AA of the rectangle is given by: A=l×wA = l \times w Substitute l=94wl = 94 - w into the area formula: A=(94w)×wA = (94 - w) \times w Expanding: A=94ww2A = 94w - w^2

Step 3: Maximizing the area

The area function A=94ww2A = 94w - w^2 is a quadratic equation. To find the maximum value of AA, we find the vertex of the parabola, which occurs at: w=b2aw = \frac{-b}{2a} In the equation A=w2+94wA = -w^2 + 94w, the coefficients are a=1a = -1 and b=94b = 94. So: w=942×1=942=47w = \frac{-94}{2 \times -1} = \frac{94}{2} = 47

Step 4: Finding the dimensions

When w=47w = 47, substitute this back into l=94wl = 94 - w to find the length: l=9447=47l = 94 - 47 = 47

Thus, the rectangle with the largest area is a square with dimensions 47×4747 \times 47.

Step 5: Writing the answer as fractions

Since the dimensions are already whole numbers, the answer in fractional form (if necessary) would be: 471×471\frac{47}{1} \times \frac{47}{1}

Final Answer:

The dimensions of the rectangle with the largest area are 471×471\frac{47}{1} \times \frac{47}{1} or simply 47×4747 \times 47.

Would you like more details on this? Here are some related questions to explore:

  1. How do you determine the maximum or minimum of a quadratic function?
  2. What is the significance of the fact that the largest-area rectangle is a square?
  3. How can we use calculus to verify that w=47w = 47 gives a maximum area?
  4. How does the perimeter affect the shape of a rectangle with maximum area?
  5. What are some practical applications of this type of optimization problem?

Tip: In optimization problems, if you're maximizing or minimizing a quantity, always check if the function you're working with is quadratic, as it will simplify finding the solution!

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Math Problem Analysis

Mathematical Concepts

Algebra
Optimization
Geometry

Formulas

Perimeter of a rectangle: P = 2l + 2w
Area of a rectangle: A = l * w
Vertex of a quadratic function: x = -b / 2a

Theorems

Quadratic optimization for maximum/minimum values

Suitable Grade Level

Grades 9-10