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Ch. 4 - Applications of Derivatives
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 4, Problem 4.3.50a

Identifying Extrema


In Exercises 41–52:


a. Identify the function’s local extreme values in the given domain, and say where they occur.


f(x) = √(x² − 2x − 3), 3 ≤ x < ∞

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Step 1: Begin by understanding the function f(x) = √(x² − 2x − 3). This is a square root function, and we need to ensure the expression inside the square root is non-negative for the function to be defined.
Step 2: Set the expression inside the square root greater than or equal to zero: x² − 2x − 3 ≥ 0. Solve this inequality to find the domain where the function is defined.
Step 3: Factor the quadratic expression: x² − 2x − 3 = (x - 3)(x + 1). Use this factorization to solve the inequality (x - 3)(x + 1) ≥ 0. Determine the intervals where the product is non-negative.
Step 4: Analyze the critical points and endpoints within the domain 3 ≤ x < ∞. Critical points occur where the derivative is zero or undefined. Find the derivative of f(x) and solve for x where f'(x) = 0 or is undefined.
Step 5: Evaluate the function at the critical points and endpoints to identify local extrema. Compare the values to determine the local maximum or minimum values within the given domain.

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Key Concepts

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

Local Extrema

Local extrema refer to the points in a function where it reaches a local maximum or minimum value. These points occur where the derivative of the function is zero or undefined, indicating a change in the direction of the curve. Identifying local extrema involves finding these critical points and using tests like the first or second derivative test to determine their nature.
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Finding Extrema Graphically

Domain of a Function

The domain of a function is the set of all possible input values (x-values) for which the function is defined. In this problem, the domain is specified as 3 ≤ x < ∞, meaning we only consider x-values starting from 3 and extending to infinity. Understanding the domain is crucial for correctly identifying where extrema can occur within the given constraints.
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Finding the Domain and Range of a Graph

Derivative and Critical Points

The derivative of a function provides the rate of change of the function with respect to its variable. Critical points occur where the derivative is zero or undefined, indicating potential local maxima or minima. To find these points, differentiate the function and solve for x where the derivative equals zero or does not exist, considering the given domain.
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Critical Points
Related Practice
Textbook Question

Finding Antiderivatives

In Exercises 1–16, find an antiderivative for each function. Do as many as you can mentally. Check your answers by differentiation.

(2/3)x⁻¹ᐟ³

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Textbook Question

51. Frictionless cart A small frictionless cart, attached to the wall by a spring, is pulled 10 cm from its rest position and released at time t = 0 to roll back and forth for 4 sec. Its position at time t is s = 10 cos πt.

a. What is the cart's maximum speed? When is the cart moving that fast? Where is it then? What is the magnitude of the acceleration then?

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Textbook Question

Identifying Extrema


In Exercises 19–40:


a. Find the open intervals on which the function is increasing and those on which it is decreasing.


f(r) = 3r³ + 16r

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Textbook Question

Identifying Extrema


In Exercises 53–60:


a. Find the local extrema of each function on the given interval, and say where they occur.


f(x) = csc²x − 2cot x, 0 < x < π

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Textbook Question

25. Paper folding A rectangular sheet of 8.5-in.-by-11-in. paper is placed on a flat surface. One of the corners is placed on the opposite longer edge, as shown in the figure, and held there as the paper is smoothed flat. The problem is to make the length of the crease as small as possible. Call the length L. Try it with paper.

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a. Show that L^2=2x^3/(2x-8.5).

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Textbook Question

Identifying Extrema


In Exercises 41–52:


a. Identify the function’s local extreme values in the given domain, and say where they occur.


g(x) = x² − 4x + 4, 1 ≤ x < ∞

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