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: 15

Answer

$3$

Work Step by Step

The domain of the variable requires that $x-1>0$. This means that $x>1$. Recall: $\log_a M^r = r \log_a M$ Using the rule above gives: $3 \log_2 (x-1) = \log_2 (x-1)^3$ Thus, the given equation is equivalent to: $\log_2{(x-1)^3}+\log_2{4}=5$ Recall further that: $\log_a (MN) = \log_a M+\log_a N$ Hence, the equation above is equivalent to: $\log_2 4(x-1)^3=5$ Since $y = \log_a b \text{ is equivalent to } b=a^y$, then $\log_2 4(x-1)^3 = 5 \text{is equivalent to } 4(x-1)^3 = 2^5$ Solve the equation to obtain: $4(x-1)^3 = 32$ $(x-1)^3 = \dfrac{32}{4}$ $(x-1)^3 = 8$ $x-1 = \sqrt[3]{8}$ $x-1 = 2$ $x = 2+1$ $x=\boxed{3}$
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