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. ln(x−2)−ln(x+3)=ln(x−1)−ln(x+7)
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 94
Textbook Question
Solve each equation. 3x+2 ⋅ 3x=81
Verified step by step guidance1
Recognize that the equation involves exponential expressions with the same base, which is 3: \(3^{x+2} \cdot 3^{x} = 81\).
Use the property of exponents that states when multiplying like bases, you add the exponents: \(3^{x+2} \cdot 3^{x} = 3^{(x+2) + x} = 3^{2x+2}\).
Rewrite the right side of the equation, 81, as a power of 3. Since \$81 = 3^4\(, the equation becomes \)3^{2x+2} = 3^4$.
Set the exponents equal to each other because the bases are the same: \$2x + 2 = 4$.
Solve the linear equation for \(x\): subtract 2 from both sides to get \$2x = 2\(, then divide both sides by 2 to find \)x$.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Properties of Exponents
This concept involves rules for manipulating expressions with exponents, such as multiplying powers with the same base by adding their exponents. For example, 3^(x+2) * 3^x equals 3^[(x+2) + x] = 3^(2x+2). Understanding these properties simplifies solving exponential equations.
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Rational Exponents
Expressing Numbers as Powers of the Same Base
To solve exponential equations, it helps to rewrite constants as powers of the same base as the variable terms. Here, 81 can be expressed as 3^4, allowing the equation to be set with equal bases and exponents, facilitating the solution.
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Solving Linear Equations
After equating the exponents, the problem reduces to solving a linear equation in terms of x. This involves isolating x by performing algebraic operations such as addition, subtraction, multiplication, or division to find its value.
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