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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
All textbooksBriggs 3rd EditionCh. 4 - Applications of the DerivativeProblem 4.8.48
Chapter 4, Problem 4.8.48

{Use of Tech} Fixed points An important question about many functions concerns the existence and location of fixed points. A fixed point of f is a value of x that satisfies the equation f(x) = x; it corresponds to a point at which the graph of f intersects the line y = x. Find all the fixed points of the following functions. Use preliminary analysis and graphing to determine good initial approximations.


f(x) = x³ - 3x² + x + 1

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Understand the concept of a fixed point: A fixed point of a function f(x) is a value x such that f(x) = x. This means the function's output is equal to its input.
Set up the equation for fixed points: For the function f(x) = x³ - 3x² + x + 1, we need to solve the equation x³ - 3x² + x + 1 = x.
Simplify the equation: Subtract x from both sides to get x³ - 3x² + x + 1 - x = 0, which simplifies to x³ - 3x² + 1 = 0.
Analyze the simplified equation: Look for possible rational roots using the Rational Root Theorem, which suggests that any rational root, in the form of a fraction p/q, is a factor of the constant term (1) divided by a factor of the leading coefficient (1). This means potential rational roots are ±1.
Graph the function or use numerical methods: Plot the function y = x³ - 3x² + 1 to visually identify where it intersects the x-axis, or use numerical methods like the Newton-Raphson method to approximate the roots. These roots are the fixed points of the function.

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Key Concepts

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

Fixed Points

A fixed point of a function f is a value x such that f(x) = x. This means that when the function is applied to this value, it returns the same value. Graphically, fixed points are where the graph of the function intersects the line y = x. Identifying fixed points is crucial in various applications, including iterative methods and stability analysis.
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Graphing Functions

Graphing functions involves plotting the function on a coordinate plane to visualize its behavior. This technique helps in identifying key features such as intercepts, maxima, minima, and fixed points. By graphing the function alongside the line y = x, one can easily observe where the two graphs intersect, indicating the fixed points of the function.
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Preliminary Analysis

Preliminary analysis refers to the initial examination of a function to gather insights about its behavior before performing detailed calculations. This may include evaluating the function at specific points, determining its derivative, and analyzing its continuity and limits. Such analysis can provide good initial approximations for fixed points, guiding further numerical methods or graphing efforts.
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Related Practice
Textbook Question

23–68. Indefinite integrals Determine the following indefinite integrals. Check your work by differentiation.


∫ (eˣ⁺²) dx

Textbook Question

{Use of Tech} Fixed points An important question about many functions concerns the existence and location of fixed points. A fixed point of f is a value of x that satisfies the equation f(x) = x; it corresponds to a point at which the graph of f intersects the line y = x. Find all the fixed points of the following functions. Use preliminary analysis and graphing to determine good initial approximations.


f(x) = tan x/2 on (-π,π)

Textbook Question

Increasing and decreasing functions. Find the intervals on which f is increasing and the intervals on which it is decreasing.


f(x) = x² - 2 ln x

Textbook Question

Locating critical points Find the critical points of the following functions. Assume a is a nonzero constant.


ƒ(x) = 1 / x + ln x

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Textbook Question

Locating critical points Find the critical points of the following functions. Assume a is a nonzero constant.


ƒ(x) = x √(x-a)

Textbook Question

17–83. Limits Evaluate the following limits. Use l’Hôpital’s Rule when it is convenient and applicable.


lim_x→ 0 (3 sin 4x) / 5x