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: 92

Answer

Solution set = $\emptyset.$

Work Step by Step

For the equation to be defined, logarithms must have positive arguments $\left[\begin{array}{lll} x-5 \gt 0, & \Rightarrow & x \gt 5\\ x+4\gt 0, & \Rightarrow & x \gt -4\\ x-1 \gt 0, & \Rightarrow & x \gt 1\\ x+2 \gt 0, & \Rightarrow & x \gt -2 \end{array}\right]$ $ x \gt 5 \qquad (*)$ This is the condition eventual solutions must satisfy. $\ln(x-5)-\ln(x+4)=\ln(x-1)-\ln(x+2)$ Apply the quotient rule on both sides: $\displaystyle \ln\frac{x-5}{x+4}=\ln\frac{x-1}{x+2}$ Recall that ln is one to one: $\displaystyle \frac{x-5}{x+4}=\frac{x-1}{x+2}$ Multiply with the LCD, $(x+4)(x+2)$: $(x-5)(x+2)=(x+4)(x-1)$ $ x^{2}-3x-10=x^{2}+3x-4$ $-3x-3x=-4+10$ $-6x=6$ $ x=-1 \quad $ ... does not satisfy (*) Thus, the solution set = $\emptyset.$
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