Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 11 - Infinite Sequences and Series - 11.1 Exercises - Page 725: 55

Answer

The sequence diverges.

Work Step by Step

By definition $n!=1 \times 2 \times 3... \times (n-1) \times n$ $\lim\limits_{n \to \infty} \frac{n!}{2^{n}}$ $=\lim\limits_{n \to \infty} \frac{1 \times 2 \times 3... \times (n-1) \times n}{2 \times 2 \times 2... \times 2 \times 2}$ $=\lim\limits_{n \to \infty} \frac{1}{2} \times \frac{2}{2} \times \frac{3}{2}... \times \frac{n-1}{2} \times \frac{n}{2}$ $=\lim\limits_{n \to \infty} \frac{1}{2} \times \frac{2}{2} \times [\frac{3}{2}... \times \frac{n-1}{2} \times \frac{n}{2}]$ The part in brackets is a product of infinity and greater than 1, therefore the part in brackets equals to $\infty$ $=\lim\limits_{n \to \infty} \frac{1}{2} \times \frac{2}{2} \times \infty = \infty$ The sequence diverges.
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