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# 4: Functions

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• 4.1: Introduction to Functions
Our development of the function concept is a modern one, but quite quick, particularly in light of the fact that today’s definition took over 300 years to reach its present state. We begin with the definition of a relation.
• 4.2: Relations and Functions
• 4.3: Interpreting the Graph of a Function
In the previous section, we began with a function and then drew the graph of the given function. In this section, we will start with the graph of a function, then make a number of interpretations based on the given graph: function evaluations, the domain and range of the function, and solving equations and inequalities.
• 4.4: The Toolbox Functions
• 4.5: Linear Functions - Applications
The ordered pairs given by a linear function represent points on a line. Linear functions can be represented in words, function notation, tabular form, and graphical form. The rate of change of a linear function is also known as the slope. An equation in the slope-intercept form of a line includes the slope and the initial value of the function. The initial value, or y-intercept, is the output value when the input of a linear function is zero.
• 4.6: Linear Functions - Calculations
• 4.7: Quadratic Functions
You may recall studying quadratic equations in Intermediate Algebra. In this section, we review those equations in the context of our next family of functions: the quadratic functions.
• 4.8: The Square Root Function
In this section we turn our attention to the square root function, the function defined by the equation f(x)=√x. We begin the section by drawing the graph of the function, then we address the domain and range. After that, we’ll investigate a number of different transformations of the function.
• 4.9: Absolute Value Functions
There are a few ways to describe what is meant by the absolute value |x| of a real number x. The long and short of both of these procedures is that |x| takes negative real numbers and assigns them to their positive counterparts while it leaves positive numbers alone. This last description is the one we shall adopt, and is summarized and discuss in this Module.
• 4.10: Exponential Functions
• 4.11: Regression
In this section, we use some basic tools from statistical analysis to quantify linear and quadratic trends that we may see in real world data in order to generate linear and quadratic models. Our goal is to give the reader an understanding of the basic processes involved, but we are quick to refer the reader to a more advanced course for a complete exposition of this material.