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Ch. 4 - Applications of the Derivative
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook
Chapter 4, Problem 4.4.8a

Sketch a graph of a function f with the following properties.


f' < 0 and f" < 0, for x < -1

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1
Understand the given conditions: f'(x) < 0 implies the function f is decreasing, and f''(x) < 0 implies the function is concave down for x < -1.
For x < -1, since f'(x) < 0, the slope of the tangent line to the graph of f is negative, meaning the graph is sloping downward.
For x < -1, since f''(x) < 0, the graph is concave down, meaning it curves downward like an upside-down bowl.
Combine the two properties: The graph of f for x < -1 should be a decreasing curve that is concave down. This means the graph slopes downward and becomes steeper as x decreases.
Sketch the graph: Start at x = -1 and draw a curve that decreases and bends downward as x moves to the left. Ensure the curve reflects both the decreasing nature (f'(x) < 0) and the concave down property (f''(x) < 0).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

First Derivative Test

The first derivative of a function, denoted as f', indicates the slope of the tangent line to the graph of the function at any point. If f' < 0, the function is decreasing in that interval. Understanding this concept is crucial for sketching the graph, as it informs us that the function is moving downward for x < -1.
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The First Derivative Test: Finding Local Extrema

Second Derivative Test

The second derivative, denoted as f'', provides information about the concavity of the function. If f'' < 0, the function is concave down, meaning that the slope of the tangent line is decreasing. This concept is essential for understanding how the graph behaves in the specified interval, indicating that the function is not only decreasing but also bending downwards.
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The Second Derivative Test: Finding Local Extrema

Graph Behavior

The overall behavior of a graph is influenced by both the first and second derivatives. In this case, since f' < 0 and f'' < 0 for x < -1, the graph will show a downward slope that becomes steeper as x decreases. Recognizing this behavior helps in accurately sketching the function, ensuring it reflects the properties of being decreasing and concave down.
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Graphing The Derivative
Related Practice
Textbook Question

Explain why or why not Determine whether the following statements are true and give an explanation or counterexample.


a. F(x) = x³ - 4x + 100 and G(x) = x³ - 4x - 100 are antiderivatives of the same function.

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Textbook Question

Folded boxes


a. Squares with sides of length x are cut out of each corner of a rectangular piece of cardboard measuring 5 ft by 8 ft. The resulting piece of cardboard is then folded into a box without a lid. Find the volume of the largest box that can be formed in this way.

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Textbook Question

Rectangles beneath a line


a. A rectangle is constructed with one side on the positive x-axis, one side on the positive y-axis, and the vertex opposite the origin on the line y = 10 - 2x. What dimensions maximize the area of the rectangle? What is the maximum area?

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Textbook Question

Maximizing profit Suppose a tour guide has a bus that holds a maximum of 100 people. Assume his profit (in dollars) for taking people on a city tour is P(n) = n(50 - 0.5n) - 100. (Although P is defined only for positive integers, treat it as a continuous function.)


a. How many people should the guide take on a tour to maximize the profit?

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Textbook Question

Population models The population of a species is given by the function P(t) = Kt²/(t² + b) , where t ≥ 0 is measured in years and K and b are positive real numbers.


a. With K = 300 and b = 30, what is lim_t→∞ P(t), the carrying capacity of the population?

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Textbook Question

Suppose the objective function P= xy is subject to the constraint 10x + y = 100, where x and y are real numbers.


a. Eliminate the variable y from the objective function so that P is expressed as a function of one variable x.

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