Express 0.314141414… as a ratio of two integers.
Ch. 10 - Sequences and Infinite Series
10장, 문제 10.R.49
42–76. Convergence or divergence Use a convergence test of your choice to determine whether the following series converge.
∑ (from k = 1 to ∞)k⁴ / √(9k¹² + 2)
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First, write down the general term of the series: \(a_k = \frac{k^4}{\sqrt{9k^{12} + 2}}\).
To analyze convergence, simplify the expression inside the square root for large \(k\). Notice that \$9k^{12}\( dominates \(2\), so approximate the denominator as \(\sqrt{9k^{12}} = 3k^6\) for large \)k$.
Rewrite the term using this approximation: \(a_k \approx \frac{k^4}{3k^6} = \frac{1}{3k^2}\) for large \(k\).
Recognize that the series behaves like \(\sum \frac{1}{k^2}\) for large \(k\), which is a p-series with \(p=2\).
Since a p-series \(\sum \frac{1}{k^p}\) converges if \(p > 1\), conclude that the original series converges by the Comparison Test.

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주요 개념
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Convergence and Divergence of Infinite Series
An infinite series converges if the sum of its terms approaches a finite limit as the number of terms grows indefinitely. If the sum does not approach a finite value, the series diverges. Understanding this distinction is fundamental to analyzing series behavior.
추천 영상:
가이드 코스
Convergence of an Infinite Series
Comparison Test for Series Convergence
The Comparison Test involves comparing the given series to a second series with known convergence properties. If the terms of the given series are smaller than those of a convergent series, it also converges; if larger than a divergent series, it diverges. This test is useful when terms resemble simpler series.
추천 영상:
가이드 코스
Direct Comparison Test
Asymptotic Behavior and Simplification of Terms
Analyzing the dominant terms in the numerator and denominator for large k helps simplify the general term of the series. This simplification reveals the term's growth rate, which is crucial for applying convergence tests effectively, such as comparing to p-series or geometric series.
추천 영상:
가이드 코스
Asymptotes of Hyperbolas
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∑ (from k = 1 to ∞)(−1)ᵏ⁺¹ / k³⁄⁷
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