Ch. 4 - Applications of the Derivative

Briggs - Calculus: Early Transcendentals 3rd Edition

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Briggs 3rd Edition

Ch. 4 - Applications of the Derivative

Problem 4.R.56

Chapter 4, Problem 4.R.56

{Use of Tech} Newton’s method Use Newton’s method to approximate the roots of ƒ(x) = e⁻²ˣ + 2eˣ - 6 to six digits.

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Identify the function for which we want to find the roots: \( f(x) = e^{-2x} + 2e^x - 6 \).

Compute the derivative of the function, \( f'(x) \), which is necessary for Newton's method. The derivative is \( f'(x) = -2e^{-2x} + 2e^x \).

Choose an initial guess \( x_0 \) for the root. A good starting point can be found by graphing the function or using prior knowledge about the behavior of exponential functions.

Apply Newton's method formula: \( x_{n+1} = x_n - \frac{f(x_n)}{f'(x_n)} \). Substitute \( f(x) \) and \( f'(x) \) into the formula to get \( x_{n+1} = x_n - \frac{e^{-2x_n} + 2e^{x_n} - 6}{-2e^{-2x_n} + 2e^{x_n}} \).

Iterate the process: Use the formula from the previous step to calculate \( x_1, x_2, \ldots \) until the difference between successive approximations is less than the desired tolerance (e.g., \( 10^{-6} \) for six-digit accuracy).

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Key Concepts

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

Newton's Method

Newton's Method is an iterative numerical technique used to approximate the roots of a real-valued function. Starting with an initial guess, the method uses the function's derivative to refine the guess iteratively. The formula is x_{n+1} = x_n - f(x_n)/f'(x_n), where x_n is the current approximation. This process is repeated until a sufficiently accurate value is found.

Exponential Functions

Exponential functions, such as e^x, are mathematical functions where the variable is in the exponent. They are characterized by rapid growth or decay, depending on the sign of the exponent. In the given function, e⁻²ˣ and eˣ represent exponential decay and growth, respectively, which influence the behavior and shape of the function's graph.

Derivative Calculation

Calculating the derivative is essential in Newton's Method as it provides the slope of the tangent line at a given point. For the function ƒ(x) = e⁻²ˣ + 2eˣ - 6, the derivative is found using the rules of differentiation for exponential functions. This derivative is crucial for updating the approximation of the root in each iteration of Newton's Method.

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