Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 3 - Section 3.4 - Exponential and Logarithmic Equations - Exercise Set - Page 489: 77

Answer

Solution set = $\displaystyle \{\frac{4}{3}\}.$

Work Step by Step

For the equation to be defined, logarithms must have positive arguments $\left[\begin{array}{llll} x+4 \gt 0, & and & x \gt 0 & \\ x \gt -4 & & & \end{array}\right]$ $ x \gt 0 \qquad (*)$ This is the condition eventual solutions must satisfy. $\log(x+4)=\log x+\log 4\qquad $... RHS: product rule $\log(x+4)=\log(x\cdot 4)\quad $ ... $\log $ is one-to-one $ x+4=4x $ $4=3x $ $ x=\displaystyle \frac{4}{3}\qquad $ ... satisfies (*) Thus, the solution set = $\displaystyle \{\frac{4}{3}\}.$
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