Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

Published by Pearson
ISBN 10: 0-32184-874-8
ISBN 13: 978-0-32184-874-1

Chapter 12 - Exponential Functions and Logarithmic Functions - Test: Chapter 12 - Page 845: 36

Answer

$x=-309,\text{ }316$

Work Step by Step

Since $\log_b y=x$ implies $b^x=y,$ the given equation, $ \log_5 |2x-7|=4,$ is equivalent to \begin{align*}\require{cancel} 5^4&=|2x-7| \\ 625&=|2x-7| \\ |2x-7|&=625 .\end{align*} Since $|x|=c$ ($c$ is a positive constant) implies $x=c\text{ or }x=-c,$ the equation above is equivalent to \begin{align*} 2x-7&=625 \text{ or }2x-7=-625 .\end{align*} Using the properties of equality, the solutions to the equations above are \begin{array}{l|r} 2x-7=625 & 2x-7=-625 \\ 2x=625+7 & 2x=-625+7 \\ 2x=632 & 2x=-618 \\\\ \dfrac{\cancel2x}{\cancel2}=\dfrac{632}{2} & \dfrac{\cancel2x}{\cancel2}=-\dfrac{618}{2} \\\\ x=316 & x=-309 .\end{array} Hence, the solutions to $\log_5 |2x-7|=4$ are $x=-309,\text{ }316$.
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