The absolute value of a number is its distance from 0 on the number line. 

The average rate of change of a function is a ratio that describes how fast one quantity changes with respect to another.  

The average rate of change for function between inputs and is the change in the outputs divided by the change in the inputs: . It is the slope of the line that connects and on the graph.

A dependent variable is a variable that represents the output of a function.

For example, the equation defines as a function of .

• The variable is called the independent variable because its value is chosen.
• The variable is called the dependent variable because it depends on . Once a value is chosen for , the value of is determined.

The domain of a function is the set of all of its possible input values.

A function is a rule that takes inputs from one set and assigns them to outputs from another set. Each input is assigned exactly one output.

Function notation is a way of writing the relationship between the inputs and outputs of a function.

For example, a function is named and is an input. Then denotes the corresponding output in function notation.

A horizontal intercept of a graph is a point where the graph crosses the horizontal axis. If the axis is labeled with the variable , a horizontal intercept is also called an -intercept. The term can also refer to only the -coordinate of the point where the graph crosses the horizontal axis.

For example, the horizontal intercept of the graph of is , or just 6.

An independent variable is a variable that represents the input of a function.

For example, the equation defines as a function of . 

• The variable is called the independent variable because its value is chosen. 
• The variable is called the dependent variable because it depends on . Once a value is chosen for , the value of is determined.

Two functions are inverses to each other if their input-output pairs are reversed.

• If one function takes as input and gives as an output, then the other function takes as an input and gives as an output.
• An inverse function can sometimes be found by reversing the processes that define the first function in order to define the second function.

For example, in the function , the input is , the number of years, and the output is , the number of weeks. The inverse function, , is the result of reversing the process of multiplying by 52. For this function, the input is , the number of weeks, and the output is , the number of years.

A linear function is a function that has a constant rate of change. This means that it grows by equal differences over equal intervals. 

For example,  defines a linear function. Any time increases by 1, increases by 4.

A maximum of a function is a value of the function that is greater than or equal to all the other values. The maximum of the function’s graph is the highest point on the graph.

A minimum of a function is a value of the function that is less than or equal to all the other values. The minimum of the function’s graph is the lowest point on the graph.

A piecewise function is a function defined using different expressions for different intervals in its domain.

The range of a function is the set of all of its possible output values.

The vertex of the graph of a quadratic function or of an absolute value function is the point where the graph changes from increasing to decreasing, or vice versa. It is the highest or lowest point on the graph.

A vertical intercept of a graph is a point where the graph crosses the vertical axis. If the axis is labeled with the variable , a vertical intercept is also called a -intercept. The term can also refer to only the -coordinate of the point where the graph crosses the vertical axis. 

For example, the vertical intercept of the graph of is , or just -5.