Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 4 - Inverse, Exponential, and Logarithmic Functions - 4.5 Exponential and Logarithmic Equations - 4.5 Exercises: 69

Answer

$x_{1}=-4;x_{2}=25$

Work Step by Step

$\log x+\log \left( x-21\right) =\log 100\Rightarrow \log \left( x\left( x-21\right) \right) =\log 100$ $\Rightarrow x^{2}-21x=100\Rightarrow x^{2}-21x-100=0\Rightarrow \left( x+4\right) \left( x-25\right) =0;x_{1}=-4;x_{2}=25$
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