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Logarithmic Functions
The logarithm of a number is the exponent by which another fixed value, the base, has to be raised to produce that number.
Learning Objective

Identify the parts of a logarithmic function and their characteristics
Key Points
 The inverse of the logarithmic operation is exponentiation.
 The logarithm is commonly used in many fields: that with base 2 in computer science, that with base e in pure mathematics and financial mathematics, and that with base 10 in natural science and engineering.
Terms

exponentiation
The process of calculating a power by multiplying together a number of equal factors, where the exponent specifies the number of factors to multiply.

exponent
The power to which a number, symbol, or expression is to be raised. For example, the 3 in
$x^3$ . 
logarithm
The logarithm of a number is the exponent by which another fixed value, the base, has to be raised to produce that number.
Full Text
Exponents and Logarithms
Introduction
In its simplest form, a logarithm is an exponent. Taking the logarithm of a number, one finds the exponent to which a certain value, known as a base, is raised to produce that number once more.
Logarithms have the following structure:
Note that
Commonly Used Bases
A logarithm with a base of 10 is called a common logarithm and is denoted simply as
A logarithm with a base of
A logarithm with a base of
The Exponential and Logarithmic Forms of an Equation
Logarithmic equations can be written as exponential equations and vice versa. The logarithmic equation
As an example, the logarithmic equation
Example 1: Solve for
Here we are looking for the exponent to which 3 is raised to yield 243. It might be more familiar if we convert the equation to exponential form giving us:
The explanation of the previous example reveals the inverse of the logarithmic operation: exponentiation. Starting with 243, if we take its logarithm with base 3, then raise 3 to the logarithm, we will once again arrive at 243.
Trivial Logarithmic Identities
The following two logarithmic identities can be verified by converting the logarithmic equation into an exponential equation as follows.
Applications of Logarithms
Historically, logarithms were invented by John Napier as a way of doing lengthy arithmetic calculations prior to the invention of the modern day calculator.
More recently, logarithms are most commonly used to simplify complex calculations that involve highlevel exponents. In chemistry, for example, pH and pKa are used to simplify concentrations and dissociation constants, respectively, of high exponential value. The purpose is to bring wideranging values into a more manageable scope. A dissociation constant may be smaller than 10^{10}, or higher than 10^{50}. Taking the logarithm of each brings the values into a more comprehensible scope (10 to 50) .
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Key Term Reference
 Interest
 Appears in these related concepts: Interest Compounded Continuously, Accounting for Interest Earned and Principal at Maturity, and Tax Considerations
 arithmetic
 Appears in these related concepts: Sums and Series, Sums, Differences, Products, and Quotients, and Arithmetic Sequences
 base
 Appears in these related concepts: Temple Architecture in the Greek Orientalizing Period, Changing Logarithmic Bases, and Rational Exponents
 complex
 Appears in these related concepts: Transduction of Sound, Introduction to Complex Numbers, and Electron Transport Chain
 compound
 Appears in these related concepts: Molecules, Compound Inequalities, and Hyphens
 compound interest
 Appears in these related concepts: Calculating Future Value, Calculating Present Value, and MultiPeriod Investment
 constant
 Appears in these related concepts: Graphing Quadratic Equations in Vertex Form, Inverse Variation, and Direct Variation
 e
 Appears in these related concepts: Natural Logarithms, Business Stakeholders: Internal and External, and The Number e
 equation
 Appears in these related concepts: Equations and Inequalities, Graphs of Equations as Graphs of Solutions, and What is an Equation?
 exponential
 Appears in these related concepts: Exponential Growth and Decay, Solving General Problems with Logarithms and Exponents, and Population Growth
 function
 Appears in these related concepts: Visualizing Domain and Range, The Vertical Line Test, and Solving Differential Equations
 indeterminate
 Appears in these related concepts: Basics of Graphing Polynomial Functions, Calculating Limits Using the Limit Laws, and Indeterminate Forms and L'Hôpital's Rule
 natural logarithm
 Appears in these related concepts: The Integral Test and Estimates of Sums, Common Bases of Logarithms, and Converting between Exponential and Logarithmic Equations
 pH
 Appears in these related concepts: AcidBase Indicators, Chemical Buffer Systems, and Financial Applications of Quadratic Functions
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Source: Boundless. “Logarithmic Functions.” Boundless Algebra. Boundless, 22 Jun. 2016. Retrieved 28 Aug. 2016 from https://www.boundless.com/algebra/textbooks/boundlessalgebratextbook/exponentslogarithmsandinversefunctions8/introductiontoexponentsandlogarithms353/logarithmicfunctions1745869/