Ch. 4 - Exponential and Logarithmic Functions

Blitzer8th EditionCollege AlgebraISBN: 9780136970514Not the one you use?Change textbook

Blitzer 8th Edition

Ch. 4 - Exponential and Logarithmic Functions

Problem 77

Chapter 5, Problem 77

Solve each logarithmic equation in Exercises 49–92. Be sure to reject any value of x that is not in the domain of the original logarithmic expressions. Give the exact answer. Then, where necessary, use a calculator to obtain a decimal approximation, correct to two decimal places, for the solution. log(x+4)=log x+log 4

Verified step by step guidance

Start with the given equation: \(\log(x+4) = \log x + \log 4\).

Use the logarithm property that states \(\log a + \log b = \log(ab)\) to combine the right side: \(\log(x+4) = \log(4x)\).

Since the logarithms are equal and the log function is one-to-one, set the arguments equal: \(x + 4 = 4x\).

Solve the resulting linear equation for \(x\): subtract \(x\) from both sides to get \(4 = 3x\), then divide both sides by 3 to find \(x = \frac{4}{3}\).

Check the domain restrictions: the arguments of the logarithms must be positive, so verify that \(x > 0\) and \(x + 4 > 0\). Since \(x = \frac{4}{3}\) satisfies these, it is a valid solution.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Properties of Logarithms

Understanding the properties of logarithms, such as the product, quotient, and power rules, is essential. In this problem, the product rule (log a + log b = log(ab)) allows combining terms on one side to simplify the equation and solve for x.

Domain of Logarithmic Functions

The domain of a logarithmic function includes only positive arguments. When solving logarithmic equations, it is crucial to check that the solutions do not make any logarithm's argument zero or negative, as these values are not valid.

Solving Logarithmic Equations

Solving logarithmic equations often involves rewriting the equation using logarithm properties, then converting to exponential form or simplifying to isolate the variable. After finding potential solutions, verify them against the domain restrictions.

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Related Practice

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In Exercises 71–78, use common logarithms or natural logarithms and a calculator to evaluate to four decimal places. log_0.1 17

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Use a graphing utility and the change-of-base property to graph each function. y = log₃ x

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In Exercises 74–79, solve each logarithmic equation. log₄ (2x+1) = log₄ (x-3) + log₄ (x+5)

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In Exercises 74–79, solve each logarithmic equation. log2 (x+3) + log2 (x-3) =4

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Use common logarithms or natural logarithms and a calculator to evaluate to four decimal places. log_π 63

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Find the domain of each logarithmic function. f(x) = log (2 - x)

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