Use the various properties of exponential and logarithmic functions to evaluate the expressions in parts (a)–(c). Given ƒ(x) = log2 x, find ƒ(2log_2 2)
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Properties of Logarithms
Problem 100
Textbook Question
Work each problem. Which of the following is equivalent to ln(4x) - ln(2x) for x > 0? A. 2 ln x B. ln 2x C. (ln 4x)/(ln 2x) D. ln 2
Verified step by step guidance1
Recall the logarithmic property that states: \(\ln a - \ln b = \ln \left( \frac{a}{b} \right)\) for positive values of \(a\) and \(b\).
Apply this property to the expression \(\ln(4x) - \ln(2x)\) by writing it as \(\ln \left( \frac{4x}{2x} \right)\).
Simplify the fraction inside the logarithm: \(\frac{4x}{2x} = 2\) since \(x > 0\) and cancels out.
Rewrite the expression as \(\ln(2)\) after simplification.
Compare the simplified expression \(\ln(2)\) with the given options to identify the equivalent expression.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Properties of Logarithms
Logarithms have specific properties that simplify expressions, such as the difference rule: ln(a) - ln(b) = ln(a/b). This property allows combining or breaking down logarithmic expressions by converting subtraction into division inside a single logarithm.
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Domain Restrictions for Logarithmic Functions
The argument of a logarithm must be positive, so for ln(4x) and ln(2x), x must be greater than zero. Understanding domain restrictions ensures the expression is valid and helps avoid undefined values during simplification.
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Simplifying Algebraic Expressions Inside Logarithms
When simplifying ln(4x) - ln(2x), use algebraic manipulation inside the logarithm: (4x)/(2x) simplifies to 2, since x > 0. Recognizing how to simplify fractions inside logarithms is key to finding the equivalent expression.
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