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Of all rectangles with a perimeter of 10, which one has the maximum area? (Give the dimensions.)

Short Answer

Expert verified
Answer: The dimensions of the rectangle with the maximum area, given a perimeter of 10 units, are length = 2.5 units and width = 2.5 units.

Step by step solution

01

Write down the formula for the perimeter of a rectangle

The formula for the perimeter (P) of a rectangle is given by P = 2 * (length + width), where length and width are the dimensions of the rectangle.
02

Express the width in terms of the length and the given perimeter

We have the perimeter, P = 10. Substitute this value into the formula and solve for the width (w): 10 = 2 * (length + width) => length + width = 5 => width = 5 - length
03

Write down the formula for the area of a rectangle

The formula for the area (A) of a rectangle is given by A = length * width.
04

Express the area in terms of the length

Substitute the expression for width (from Step 2) into the area formula: A = length * (5 - length).
05

Find the critical points to determine the maximum area

To find the critical points, take the first derivative of the area function with respect to the length and set it equal to 0: \(\frac{dA}{dlength} = 5-2*length = 0\) => \(length = 2.5\)
06

Find the width for the maximum area

Substitute the value for the critical length into the expression for the width (from Step 2): width = 5 - 2.5 = 2.5
07

State the dimensions of the rectangle with the maximum area

The dimensions of the rectangle with the maximum area, given a perimeter of 10, are length = 2.5 units and width = 2.5 units.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Optimization in Calculus
Understanding optimization in calculus is essential when solving problems like finding the rectangle with the maximum area given a fixed perimeter. Optimization is the process of determining the best, most efficient, or optimal solution from a set of possible options. In calculus, this typically involves finding the maximum or minimum values of a function.

In the given exercise, we use optimization to decide which rectangle dimensions offer the most area. To tackle such problems, we first write down the formula that needs to be optimized—in this case, the area of a rectangle. We must also consider any constraints; here, our constraint is the perimeter, which is fixed. Introducing the constraint into the formula allows us to express one variable in terms of the other, simplifying the problem to one variable. Then, we can find the function's critical points by setting its derivative equal to zero. These critical points lead us to the optimal solution.
Derivatives to Find Maximum Area
By utilizing derivatives in calculus, we can find the maximum area of shapes with certain constraints. In our original exercise, we needed to determine the dimensions that maximize the area of a rectangle with a given perimeter. After expressing the area as a function of one of its sides, the next step is to find the first derivative of the area with respect to that side.

The derivative of the area function represents the rate of change of the area with respect to the rectangle's length. Setting this derivative equal to zero allows us to locate the critical points. In optimization problems, these critical points represent possible maximum or minimum values of the function. By examining these points, we can determine whether they correspond to a maximum, which in this example, results in a square with equal length and width, representing the rectangle with the most area under the given conditions.
Rectangle Properties
The properties of rectangles are pivotal in addressing geometry optimization problems. A rectangle is characterized by having four sides, with opposite sides being both parallel and equal in length, and all of its angles as right angles. Because of these properties, the formulas for the area and perimeter of a rectangle are straightforward: the area is the product of its length and width, and the perimeter is twice the sum of its length and width.

When given the perimeter, as in the textbook exercise, we can use the properties of rectangles to express one dimension in terms of the other. In the optimization process, when we discover that a rectangle with maximum area for a given perimeter is a square, it directly relates to the rectangle’s properties. This is because a square, a special case of a rectangle, guarantees that the area is as large as possible when distributing a fixed perimeter evenly among all four sides.

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