Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 9 - Infinite Series - 9.4 Exercises - Page 617: 40

Answer

Diverges

Work Step by Step

The given series can be summed up as: $\dfrac{1}{200}+\dfrac{1}{210}+\dfrac{1}{220}+.....=\Sigma_{n=1}^{\infty} \dfrac{1}{10 n+200}$ Let us consider that $a_n=\Sigma_{n=1}^{\infty} \dfrac{1}{10 n+200}$ and $b_n=\Sigma_{n=1}^{\infty} \dfrac{1}{n}$ We can see that $a_n \leq b_n$ and $b_n$ shows a p-series with $p=1$. This implies that the series $b_n$ diverges by the p-series test. Next, we have $\lim\limits_{n \to \infty} \dfrac{a_n}{b_n} =\lim\limits_{n \to \infty} (\dfrac{1}{10n+200}) \times n$ or, $=\lim\limits_{n \to \infty} \dfrac{n}{10 n+200}$ or, $=\lim\limits_{n \to \infty} \dfrac{1}{10+200/n}$ or, $=\dfrac{1}{10}$ Hence, we can see that the given series diverges by the limit comparison test.
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