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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 10.8.45

11–86. Applying convergence tests Determine whether the following series converge. Justify your answers.
∑ (from k = 1 to ∞) k⁴ / (eᵏ⁵)

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Identify the given series: \( \sum_{k=1}^{\infty} \frac{k^{4}}{e^{k^{5}}} \). We want to determine if this infinite series converges.
Consider the general behavior of the terms \( a_k = \frac{k^{4}}{e^{k^{5}}} \). Notice that the denominator grows exponentially with respect to \( k^{5} \), while the numerator grows polynomially as \( k^{4} \).
Apply the Comparison Test or Limit Comparison Test by comparing \( a_k \) to a simpler series. Since exponential growth dominates polynomial growth, compare \( a_k \) to \( \frac{1}{e^{k^{5}}} \), which is a convergent series because its terms approach zero very rapidly.
Since \( \sum \frac{1}{e^{k^{5}}} \) converges (it is a series with terms decreasing faster than any geometric series), and \( \frac{k^{4}}{e^{k^{5}}} \leq C \cdot \frac{1}{e^{k^{5}}} \) for some constant \( C \) and sufficiently large \( k \), by the Comparison Test, the original series converges.
Conclude that the series \( \sum_{k=1}^{\infty} \frac{k^{4}}{e^{k^{5}}} \) converges absolutely due to the dominance of the exponential term in the denominator.

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