Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 4 - Section 4.5 - Exponential and Logarithmic Functions - 4.5 Exercises - Page 368: 27

Answer

$x=\dfrac{\log\dfrac{5}{4}}{5}\approx0.019382$

Work Step by Step

$4(1+10^{5x})=9$ First, let's solve for $10^{5x}$: $1+10^{5x}=\dfrac{9}{4}$ $10^{5x}=\dfrac{9}{4}-1$ $10^{5x}=\dfrac{5}{4}$ Apply $\log$ to both sides of the equation: $\log10^{5x}=\log\dfrac{5}{4}$ The exponent $5x$ can be taken down to multiply in front of its respective $\log$: $5x\log10=\log\dfrac{5}{4}$ Since $\log10=1$, the equation becomes: $5x=\log\dfrac{5}{4}$ Solve for $x$: $x=\dfrac{\log\dfrac{5}{4}}{5}\approx0.019382$
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