Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 9 - Infinite Series - 9.5 The Comparison, Ratio, And Root Tests - Exercises Set 9.5 - Page 637: 30

Answer

Diverges

Work Step by Step

Apply the limit comparison test. Therefore, $ \lim\limits_{k \to \infty} \dfrac{a_k}{b_k}=\lim\limits_{k \to \infty} \dfrac{k^2/k^3+1}{1/k}\\=\lim\limits_{k \to \infty} \dfrac{k^3}{k^3+1}\\=\lim\limits_{k \to \infty} \dfrac{k^3+1}{k^3+1} -\dfrac{1}{k^3+1} \\=\lim\limits_{k \to \infty} 1- \dfrac{1}{k^3+1} \\=1-0\\=1 \ne 0 \ne \infty$ We can conclude that the given series diverges by the limit comparison test because $\Sigma_{n=1}^{\infty} \dfrac{1}{k}$ is a p-series with $p=1$, so it diverges.
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