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Ch. 11 - Power Series
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 11, Problema 11.2.21

Radius and interval of convergence Determine the radius and interval of convergence of the following power series.


−x²/1 + x⁴/2! −x⁶/3! + x⁸/4! − ⋯

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First, rewrite the given power series in a general term form. Notice the pattern of powers and factorials: the nth term looks like \((-1)^n \frac{x^{2(n+1)}}{(n+1)!}\), starting from \(n=0\).
Identify the general term \(a_n = (-1)^n \frac{x^{2(n+1)}}{(n+1)!}\). To analyze convergence, it is often easier to express the series as \(\sum_{n=0}^\infty (-1)^n \frac{x^{2(n+1)}}{(n+1)!}\).
Apply the Ratio Test to find the radius of convergence. Compute the limit \(L = \lim_{n \to \infty} \left| \frac{a_{n+1}}{a_n} \right|\) where \(a_n = (-1)^n \frac{x^{2(n+1)}}{(n+1)!}\).
Simplify the ratio inside the limit: \(\left| \frac{a_{n+1}}{a_n} \right| = \left| \frac{x^{2(n+2)}}{(n+2)!} \cdot \frac{(n+1)!}{x^{2(n+1)}} \right| = \left| \frac{x^2}{n+2} \right|\).
Evaluate the limit as \(n \to \infty\): \(L = \lim_{n \to \infty} \left| \frac{x^2}{n+2} \right| = 0\) for all real \(x\). Since \(L=0 < 1\) for all \(x\), the radius of convergence is infinite, meaning the series converges for all real \(x\). Thus, the interval of convergence is \((-\infty, \infty)\).

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Power Series

A power series is an infinite sum of terms in the form a_n(x - c)^n, where a_n are coefficients and c is the center. Understanding the structure of power series helps analyze their convergence behavior depending on the value of x.
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Intro to Power Series

Radius of Convergence

The radius of convergence is the distance from the center within which a power series converges absolutely. It can be found using tests like the Ratio Test or Root Test, indicating the interval where the series represents a valid function.
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Radius of Convergence

Interval of Convergence

The interval of convergence is the set of all x-values for which the power series converges. It includes the radius of convergence and requires checking endpoints separately to determine if the series converges or diverges there.
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Interval of Convergence
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Domanda del libro di testo

Remainders Find the remainder in the Taylor series centered at the point a for the following functions. Then show that lim ₙ→∞ Rₙ(x)=0, for all x in the interval of convergence.


f(x) = e⁻ˣ, a = 0

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Domanda del libro di testo

Radius and interval of convergence Determine the radius and interval of convergence of the following power series.


∑ₖ₌₀∞ (2x)ᵏ/k!

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Probability: tossing for a head The expected (average) number of tosses of a fair coin required to obtain the first head is ∑ₖ₌₁∞ k(1/2)ᵏ. Evaluate this series and determine the expected number of tosses. (Hint: Differentiate a geometric series.) 

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Any method


a. Use any analytical method to find the first four nonzero terms of the Taylor series centered at 0 for the following functions. You do not need to use the definition of the Taylor series coefficients.


b. Determine the radius of convergence of the series.


f(x) = (1 + x²)⁻²/³

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Domanda del libro di testo

Manipulating Taylor series Use the Taylor series in Table 11.5 to find the first four nonzero terms of the Taylor series for the following functions centered at 0.


ln (1 + x²)

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Use of Tech Linear and quadratic approximation


a. Find the linear approximating polynomial for the following functions centered at the given point a.


b. Find the quadratic approximating polynomial for the following functions centered at a.


c Use the polynomials obtained in parts (a) and (b) to approximate the given quantity.


f(x) = cos x, a = π/4; approximate cos (0.24π)

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