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. log3(x+6)+log3(x+4)=1
Table of contents
- 0. Review of Algebra4h 18m
- 1. Equations & Inequalities3h 18m
- 2. Graphs of Equations1h 43m
- 3. Functions2h 17m
- 4. Polynomial Functions1h 44m
- 5. Rational Functions1h 23m
- 6. Exponential & Logarithmic Functions2h 28m
- 7. Systems of Equations & Matrices4h 5m
- 8. Conic Sections2h 23m
- 9. Sequences, Series, & Induction1h 22m
- 10. Combinatorics & Probability1h 45m
6. Exponential & Logarithmic Functions
Solving Exponential and Logarithmic Equations
Problem 73
Textbook Question
Solve each equation. Give solutions in exact form. ln(4x - 2) - ln 4 = -ln(x - 2)
Verified step by step guidance1
Recall the logarithmic property that allows you to combine the difference of logarithms: \(\ln a - \ln b = \ln \left( \frac{a}{b} \right)\). Apply this to the left side of the equation to combine the logarithms: \(\ln(4x - 2) - \ln 4 = \ln \left( \frac{4x - 2}{4} \right)\).
Rewrite the equation using the combined logarithm: \(\ln \left( \frac{4x - 2}{4} \right) = -\ln(x - 2)\).
Use the property that \(-\ln y = \ln \left( \frac{1}{y} \right)\) to rewrite the right side: \(\ln \left( \frac{4x - 2}{4} \right) = \ln \left( \frac{1}{x - 2} \right)\).
Since the natural logarithm function \(\ln\) is one-to-one, set the arguments equal to each other: \(\frac{4x - 2}{4} = \frac{1}{x - 2}\).
Solve the resulting rational equation for \(x\) by cross-multiplying and simplifying. Remember to check for any restrictions on \(x\) from the original logarithmic expressions to ensure the solutions are valid.
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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 difference rule ln(a) - ln(b) = ln(a/b), is essential for simplifying and combining logarithmic expressions. These properties allow you to rewrite the equation in a more manageable form to isolate the variable.
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Change of Base Property
Solving Logarithmic Equations
Solving logarithmic equations involves rewriting the equation to isolate the logarithm and then exponentiating both sides to eliminate the logarithm. This process converts the equation into an algebraic form that can be solved for the variable.
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Solving Logarithmic Equations
Domain Restrictions of Logarithmic Functions
Logarithmic functions are only defined for positive arguments. When solving equations involving logarithms, it is crucial to consider domain restrictions to ensure that the solutions do not make any logarithmic expression undefined or invalid.
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Domain Restrictions of Composed Functions
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