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: 64

Answer

$x=5$

Work Step by Step

$\log x+\log(x-3)=1$ Combine the logarithms on the left side of the equation as a product: $\log x(x-3)=1$ $\log(x^{2}-3x)=1$ Write this equation in exponential form: $x^{2}-3x=10^{1}$ $x^{2}-3x=10$ Take the $10$ to the left side of the equation: $x^{2}-3x-10=0$ Solve by factoring: $(x+2)(x-5)=0$ We get two solutions: $x=-2$ and $x=5$ The initial equation is undefined at $x=-2$, so we can discard that solution. Our final answer is $x=5$.
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