Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

Published by Pearson
ISBN 10: 0-32193-104-1
ISBN 13: 978-0-32193-104-7

Chapter 4 - Exponential and Logarithmic Functions - Section 4.6 Logarithmic and Exponential Equations - 4.6 Assess Your Understanding - Page 337: 19

Answer

$\dfrac{21}{8}$

Work Step by Step

The domain of the variable requires that $2x+1>0$ and $x-2>0$ Thus: $2x>-1 \longrightarrow x>-\dfrac{1}{2}$ $x-2 >0 \longrightarrow x>2$ Therefore, $x>2$ Rearranging the equation gives: $\log(2x+1)-\log(x-2)=1$ Since $\log_a\left(\dfrac{M}{N}\right) = \log_a M-\log_a N$, then $\therefore \log(2x+1)-\log(x-2) = \log \left(\dfrac{2x+1}{x-2} \right)$ Hence, the equation above is equivalent to: $\log \left(\dfrac{2x+1}{x-2} \right) = 1$ $\because \log_a{b} = 1 \longrightarrow a^1=b$, then \begin{align*} 10^1&=\dfrac{2x+1}{x-2}\\\\ 10&=\dfrac{2x+1}{x-2}\\\\ 2x+1 &= 10(x-2)\\\\ 2x+1&=10x-20\\\\ 1+20&=10x-2x\\\\ 21&=8x\\\\ \frac{21}{8}&=x \end{align*} Therefore, $x= \boxed{\dfrac{21}{8}}$.
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