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Ch. 10 - Sequences and Infinite Series
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243당신이 사용하는 게 아니라요?교과서 변경
10장, 문제 10.7.11

9–30. The Ratio and Root Tests Use the Ratio Test or the Root Test to determine whether the following series converge absolutely or diverge.
∑ (from k = 1 to ∞) ((-1)ᵏ⁺¹) × ((10k³ + k) / (9k³ + k + 1))ᵏ

검증된 단계별 안내
1
Identify the general term of the series: \(a_k = (-1)^{k+1} \left( \frac{10k^3 + k}{9k^3 + k + 1} \right)^k\).
Since the series has terms raised to the power \(k\), the Root Test is a natural choice. Recall the Root Test uses the limit \(L = \lim_{k \to \infty} \sqrt[k]{|a_k|}\).
Calculate \(\sqrt[k]{|a_k|}\). Because of the absolute value, the \((-1)^{k+1}\) disappears, so \(\sqrt[k]{|a_k|} = \sqrt[k]{\left( \frac{10k^3 + k}{9k^3 + k + 1} \right)^k} = \frac{10k^3 + k}{9k^3 + k + 1}\).
Evaluate the limit \(L = \lim_{k \to \infty} \frac{10k^3 + k}{9k^3 + k + 1}\). To do this, divide numerator and denominator by \(k^3\) to simplify the expression.
Interpret the result of the limit \(L\): if \(L < 1\), the series converges absolutely; if \(L > 1\), the series diverges; if \(L = 1\), the Root Test is inconclusive.

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주요 개념

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

Ratio Test

The Ratio Test determines the convergence of a series by examining the limit of the absolute value of the ratio of consecutive terms. If this limit is less than 1, the series converges absolutely; if greater than 1, it diverges; if equal to 1, the test is inconclusive.
추천 영상:

Root Test

The Root Test analyzes the nth root of the absolute value of the nth term of a series. If the limit of this root is less than 1, the series converges absolutely; if greater than 1, it diverges; if equal to 1, the test is inconclusive. It is especially useful for terms raised to the nth power.
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Absolute Convergence

A series converges absolutely if the series of absolute values of its terms converges. Absolute convergence implies convergence regardless of term signs, which is important when applying tests like the Ratio or Root Test to series with alternating signs.
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07:51
Choosing a Convergence Test