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Precalculus Essentials
Fifth Edition Chapter 3 Exponential and Logarithmic Functions If this PowerPoint presentation contains mathematical equations, you may need to check that your computer has the following installed: 1) MathType Plugin 2) Math Player (free versions available) 3) NVDA Reader (free versions available) Copyright © 2018, 2014, 2010 Pearson Education, Inc. All Rights Reserved
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3.2 Logarithmic Functions
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Objectives Change from logarithmic to exponential form.
Change from exponential to logarithmic form. Evaluate logarithms. Use basic logarithmic properties. Graph logarithmic functions. Find the domain of a logarithmic function. Use common logarithms. Use natural logarithms.
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Definition of the Logarithmic Function
For x > 0 and b > 0, b ≠ 1,
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Example: Changing from Logarithmic to Exponential Form
Write each equation in its equivalent exponential form:
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Example: Changing from Exponential to Logarithmic Form
Write each equation in its equivalent logarithmic form:
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Example 1: Evaluating Logarithms
Solution:
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Example 2: Evaluating Logarithms
Solution:
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Example 3: Evaluating Logarithms
Solution:
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Basic Logarithmic Properties Involving One
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Example: Using Properties of Logarithms
Solution:
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Inverse Properties of Logarithms
For b > 0 and b ≠ 1,
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Example: Using Inverse Properties of Logarithms
Solution:
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Example: Graphs of Exponential and Logarithmic Functions (1 of 3)
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Example: Graphs of Exponential and Logarithmic Functions (2 of 3)
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Example: Graphs of Exponential and Logarithmic Functions (3 of 3)
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Characteristics of Logarithmic Functions of the Form f(x) = logb x
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The Domain of a Logarithmic Function
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Example: Finding the Domain of a Logarithmic Function
Solution:
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Example: Illustration of the Domain of a Logarithmic Function
Solution: We found that the domain of f is (5, ∞). This is illustrated by the graph of f.
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Common Logarithms The logarithmic function with base 10 is called the common logarithmic function.
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Example 1: Application The percentage of adult height attained by a boy who is x years old can be modeled by f(x) = log(x + 1), where x represents the boy’s age (from 5 to 15) and f(x) represents the percentage of his adult height. Approximately what percentage of his adult height has a boy attained at age ten? A ten-year old boy has attained approximately 80% of his adult height.
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Properties of Common Logarithms
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Natural Logarithms The logarithmic function with base e is called the natural logarithmic function.
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Properties of Natural Logarithms
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Example 2: Application When the outside air temperature is anywhere from 72° to 96° Fahrenheit, the temperature in an enclosed vehicle climbs by 43° in the first hour. The function f(x) = 13.4 ln x − 11.6 models the temperature increase, f(x), in degrees Fahrenheit, after x minutes. Use the function to find the temperature increase, to the nearest degree, after 30 minutes. The temperature will increase by approximately 34° after 30 minutes.
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