Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 4 - Section 4.5 - Exponential and Logarithmic Functions - 4.5 Exercises - Page 368: 68

Answer

$x=3$

Work Step by Step

$\log_{3}(x+15)-\log_{3}(x-1)=2$ Combine the logarithms on the left side of the equation as a division: $\log_{3}\Big(\dfrac{x+15}{x-1}\Big)=2$ Write this equation in exponential form: $\dfrac{x+15}{x-1}=3^{2}$ $\dfrac{x+15}{x-1}=9$ Solve for $x$: $x+15=9(x-1)$ $x+15=9x-9$ $x-9x=-9-15$ $-8x=-24$ $x=\dfrac{-24}{-8}=3$
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