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Ch. 11 - Power Series
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243당신이 사용하는 게 아니라요?교과서 변경
11장, 문제 11.2.11

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


∑ₖ₌₁∞ (kx)ᵏ

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1
Identify the given power series: \( \sum_{k=1}^{\infty} (kx)^k \). This can be rewritten as \( \sum_{k=1}^{\infty} k^k x^k \).
To find the radius of convergence, use the root test which involves the limit \( L = \lim_{k \to \infty} \sqrt[k]{|a_k|} \), where \( a_k = k^k x^k \).
Calculate \( \sqrt[k]{|a_k|} = \sqrt[k]{k^k |x|^k} = k |x| \).
Find the limit \( L = \lim_{k \to \infty} k |x| \). For the series to converge, this limit must be less than 1, so set \( \lim_{k \to \infty} k |x| < 1 \).
Since \( \lim_{k \to \infty} k |x| = \infty \) for any \( x \neq 0 \), the radius of convergence is 0, meaning the series converges only at \( x = 0 \). The interval of convergence is therefore \( \{0\} \).

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Power Series

A power series is an infinite sum of terms in the form a_k(x - c)^k, where a_k are coefficients and c is the center. Understanding the structure of power series is essential to analyze their convergence behavior depending on the variable x.
추천 영상:
05:58
Intro to Power Series

Radius of Convergence

The radius of convergence is the distance from the center c within which the power series converges absolutely. It can be found using tests like the Ratio Test or Root Test, and it defines the interval where the series behaves well.
추천 영상:
07:36
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 all points within the radius of convergence and requires checking endpoints separately to determine if the series converges there.
추천 영상:
08:44
Interval of Convergence