Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 10: Infinite Sequences and Series - Section 10.1 - Sequences - Exercises 10.1 - Page 571: 112

Answer

The sequence $a_n$ is monotonic and unbounded.

Work Step by Step

Consider $a_n=\dfrac{(2n+3)!}{(n+1)!}$ for all $n \in N$ Also, $a_{n+1}=\dfrac{(2(n+1)+3)!}{((n+1)+1)!}$ and $(4n+10)\dfrac{(2n+3)!}{(n+1)!}=(4n+10) a_n$ ; for all $n \in N$ so, $1 \lt 4n+10$ for all $n \in N$ This means that $a_n \lt a_{n+1}$ for all $n \in N$ .Thus $a_n$ increases and is monotonic. To check the sequence is bounded or not.In order to find that we have $a_n \lt \dfrac{(2n+3)!}{(n+1)!}=(2n+3)(\dfrac{(2n+2)!}{(n+1)!})$ Also, $\lim\limits_{n \to \infty}2n+3=\infty$ so, $a_n$ is unbounded. Therefore, we can see that the sequence $a_n$ is monotonic and unbounded.
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