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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.31

27–37. Evaluating series Evaluate the following infinite series or state that the series diverges.
∑ (from k = 1 to ∞)ln((2k + 1) / (2k − 1))

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Start by writing out the general term of the series: \( a_k = \ln\left(\frac{2k + 1}{2k - 1}\right) \).
Use the logarithm property \( \ln\left(\frac{A}{B}\right) = \ln(A) - \ln(B) \) to rewrite the term as \( a_k = \ln(2k + 1) - \ln(2k - 1) \).
Express the partial sum \( S_n = \sum_{k=1}^n a_k \) by substituting the expanded terms: \( S_n = \sum_{k=1}^n \left( \ln(2k + 1) - \ln(2k - 1) \right) \).
Rewrite the partial sum as \( S_n = \left( \ln 3 - \ln 1 \right) + \left( \ln 5 - \ln 3 \right) + \left( \ln 7 - \ln 5 \right) + \cdots + \left( \ln(2n + 1) - \ln(2n - 1) \right) \) and observe the telescoping pattern where most terms cancel out.
Simplify the telescoping sum to \( S_n = \ln(2n + 1) - \ln 1 \), then analyze the limit \( \lim_{n \to \infty} S_n = \lim_{n \to \infty} \ln(2n + 1) \) to determine whether the series converges or diverges.

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An infinite series is the sum of infinitely many terms. To evaluate such a series, it is crucial to determine whether it converges (approaches a finite limit) or diverges (grows without bound or oscillates). Convergence tests help decide if the sum exists.
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