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: 78

Answer

Solution set = $\{5\}.$

Work Step by Step

For the equation to be defined, logarithms must have positive arguments $\left[\begin{array}{llll} 5x+1 \gt 0, & and & 2x+3 \gt 0 & \\ x \gt -1/5 & & x\gt-3/2 & \end{array}\right]$ $ x \gt -1/5 \qquad (*)$ This is the condition eventual solutions must satisfy. $\log(5x+1)=\log(2x+3)+\log 2\qquad $... RHS: product rule $\log(5x+1)=\log[(4x+6)\cdot 2]\quad $ ... $\log $ is one-to-one $5x+1=4x+6$ $5x-4x=6-1$ $ x=5\qquad $ ... satisfies (*) Thus, the solution set = $\{5\}.$
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