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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 4.8.51
Chapter 4, Problem 4.8.51

{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) = 2x cos x on [0,2]

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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 graph of f(x) intersects the line y = x at this point.
Set up the equation for fixed points: For the function f(x) = 2x cos(x), we need to solve the equation 2x cos(x) = x. This simplifies to 2x cos(x) - x = 0.
Factor the equation: The equation can be rewritten as x(2 cos(x) - 1) = 0. This gives us two potential solutions: x = 0 or 2 cos(x) - 1 = 0.
Solve the equation 2 cos(x) - 1 = 0: This simplifies to cos(x) = 1/2. Determine the values of x within the interval [0, 2] that satisfy this equation.
Use graphing or numerical methods to approximate solutions: Graph the function f(x) = 2x cos(x) and the line y = x on the interval [0, 2] to visually identify points of intersection. Alternatively, use numerical methods like the bisection method or Newton's method to find more precise values of x where f(x) = x.

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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 at this point, the output of the function equals the input. 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. For the function f(x) = 2x cos x, graphing can provide insights into where the function intersects the line y = x, aiding in the approximation of fixed points.
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Preliminary Analysis

Preliminary analysis refers to the initial examination of a function's properties, such as continuity, differentiability, and behavior over a specified interval. For the function f(x) = 2x cos x on [0, 2], this analysis can help determine the likelihood of fixed points existing within that range and guide the selection of initial approximations for further numerical methods.
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