Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 1 - Problems - Page 75: 16

Answer

$log_2 ~5$ is an irrational number.

Work Step by Step

Let's assume that $log_2 ~5$ is a rational number. Then: $log_2~5 = \frac{a}{b}$ (where $a$ and $b$ are positive integers) $2^{a/b} = 5$ $(2^a)^{1/b} = 5$ $2^a = 5^b$ However, $2^a$ is an even number while $5^b$ is an odd number. The statement $2^a=5^b$ is a contradiction. Therefore, our initial assumption must be false. Thus, $log_2 ~5$ must be an irrational number.
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