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Ch. 10 - Sequences and Infinite Series
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 10, Problema 10.4.51

48–63. Choose your test Determine whether the following series converge or diverge using the properties and tests introduced in Sections 10.3 and 10.4.
∑ (k = 1 to ∞) 1 / ( (3k + 1)(3k + 4) )

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First, recognize the series given: \( \sum_{k=1}^{\infty} \frac{1}{(3k + 1)(3k + 4)} \). This is an infinite series with positive terms, so we can consider tests for convergence of positive term series.
Next, try to simplify the general term using partial fraction decomposition. Express \( \frac{1}{(3k + 1)(3k + 4)} \) as \( \frac{A}{3k + 1} + \frac{B}{3k + 4} \) and solve for constants \( A \) and \( B \).
After finding \( A \) and \( B \), rewrite the series as \( \sum_{k=1}^{\infty} \left( \frac{A}{3k + 1} + \frac{B}{3k + 4} \right) \). This often leads to a telescoping series where many terms cancel out.
Identify the telescoping pattern by writing out the first few terms explicitly and observe how terms cancel when summed.
Finally, use the telescoping property to find the partial sums and analyze their limit as \( n \to \infty \). If the limit exists and is finite, the series converges; otherwise, it diverges.

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Convergence and Divergence of Infinite Series

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Partial Fraction Decomposition

Partial fraction decomposition breaks a complex rational expression into simpler fractions that are easier to sum or analyze. For series with terms like 1/((3k+1)(3k+4)), this technique helps rewrite terms to identify telescoping behavior or apply known convergence tests.
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