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 - Study Summary - Practice Exercises - Page 844: 64

Answer

$x=5$

Work Step by Step

We have to find x: $$\log_{3}(x-4)=2-\log_{3}(x+4)$$ $$\log_{3}(x-4)+\log_{3}(x+4)=2$$ Use the Product Property of logarithm $$\log_{3}(x-4)(x+4)=2$$ $$(x-4)(x+4)=3^2=9$$ $$x^2-16=9$$ $$x^2=9+16$$ $$x^2=25$$ $$x_{1}=5 \text{ and } x_{2}=-5$$ But $x_{2}=-5 $ is not suitable for us because the expression $\log_{a}x$ is defined only for $x>0$ and when we replace $x=-5$ in the given equation we get $\log_3 (-5-4)=\log_3(-9)$ which is not possible. For $x=5$ the logarithms are defined. So the only solution of the equation is: $$x=5$$
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