University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 9 - Section 9.1 - Sequences - Exercises - Page 489: 112

Answer

The sequence $a_n$ is monotonic and unbounded.

Work Step by Step

Our aim is to find out if the sequence $a_n$ is monotonic. In order to this, we will consider $a_n=\dfrac{(2n+3)!}{(n+1)!}$ for all $n \in N$ Also, $a_{n+1}=\dfrac{(2(n+1)+3)!}{((n+1)+1)!}=(4n+10)\dfrac{(2n+3)!}{(n+1)!}=(4n+10) a_n$ for all $n \in N$ Thus, we find that $1 \lt 4n+10$ for all $n \in N$ This implies that $a_n \lt a_{n+1}$ for all $n \in N$ and so, $a_n$ is increasing and thus, monotonic. Now, we will check for a bounded or unbounded sequence. In order to this we will take $a_n \lt \dfrac{(2n+3)!}{(n+1)!}=(2n+3)(\dfrac{(2n+2)!}{(n+1)!})$ and $\lim\limits_{n \to \infty}2n+3=\infty$ Thus, $a_n$ is unbounded. Hence, the sequence $a_n$ is monotonic and unbounded.
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