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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.R.47

42–76. Convergence or divergence Use a convergence test of your choice to determine whether the following series converge.
∑ (from k = 1 to ∞)(7 + sin k) / k²

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1
Identify the given series: \( \sum_{k=1}^{\infty} \frac{7 + \sin k}{k^2} \). We want to determine if this series converges or diverges.
Note that \( \sin k \) is bounded between -1 and 1, so the numerator \( 7 + \sin k \) is bounded between 6 and 8. This means the terms behave roughly like \( \frac{\text{constant}}{k^2} \) for large \( k \).
Recall the p-series test: \( \sum_{k=1}^{\infty} \frac{1}{k^p} \) converges if \( p > 1 \). Here, since the denominator is \( k^2 \), which corresponds to \( p = 2 > 1 \), the series \( \sum \frac{1}{k^2} \) converges.
Use the Comparison Test by comparing \( \frac{7 + \sin k}{k^2} \) with \( \frac{8}{k^2} \) (since 8 is an upper bound for the numerator). Since \( \sum \frac{8}{k^2} \) converges, and \( 0 \leq \frac{7 + \sin k}{k^2} \leq \frac{8}{k^2} \), the original series converges by the Comparison Test.
Conclude that the series \( \sum_{k=1}^{\infty} \frac{7 + \sin k}{k^2} \) converges absolutely because it is bounded by a convergent p-series with \( p = 2 \).

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