Domain & Range

Domain & Range

Site: | TBAISD Moodle |

Course: | Michigan Algebra I Preview 2012 |

Book: | Domain & Range |

Printed by: | Guest user |

Date: | Friday, April 16, 2021, 10:28 PM |

Introduction

As discussed previously, for exponential functions of the form, , there is no restriction on the value of *x*. Therefore, the function is defined for all real values of *x*, and the **domain** is .

All exponential functions have an asymptote, or line that the graph will approach but never touch or cross. Therefore, the **range** of an exponential function of the form, , is dependent on the sign of *a* and the value of the asymptote. If *a* is a positive value then the graph will approach the asymptote from the top, which means the range will be greater than the asymptote. If *a* is negative, then the graph will approach the asymptote from the bottom, which means the range will be less than the asymptote. Because the graph never intersects the asymptote, the range will never include this value.

Example 1

Find the domain and range of the function:*Step 1. *Find the domain.

Since the function is not representing a situation, the *x* can be any real number.

Therefore, the domain is .

*Step 2. *Find the range.

This graph is shifted up 2 and has an asymptote at the line y = 2. It also has a positive *a*-value.

Therefore, the range of the function is .

Example 2

Find the domain and range of the function: .*Step 1. *Find the domain.

Since the function is not representing a situation, the *x* can be any real number.

Therefore, the domain is .

*Step 2. *Find the range.

This graph is shifted to the right 2, which does not affect the asymptote. It has an asymptote at y = 0. It also has a positive *a*-value.

Therefore, the range of the function is .

Example 3

Find the domain and range of the function: .*Step 1. *Find the domain.

Since the function is not representing a situation, the *x* can be any real number.

Therefore, the domain is .

*Step 2. *Find the range.

This graph is shifted down 2 and has an asymptote at y = -2. It also has a negative *a*-value.

Therefore, the range of the function is .

From a Graph

To find domain and range of an exponential function by looking at a graph, determine where the

In the graph above, since all *x* values appear to be present in the graph, the domain is all real numbers or . Since the horizontal asymptote is *y* = 0, there will not be any values below, or at, *y* = 0. The range is *y* > 0, or .

Example

Find the domain and range of the graph below.

Since all x values appear to be present in the graph, the domain is all real numbers, or .

*Step 2. * Find the range.

Since the horizontal asymptote is y = -2, then there will not be any values below, or at, y = -2. The range is y > -2, or .

Video Lesson

To learn how to determine the domain and range of an exponential function, select the following link:Sources

Adams, R., & Free High School Science Texts.2009. Exponential Functions and Graphs - Grade 11. Connexions, July 29, 2009. http://cnx.org/content/m30856/1.1/.

Dendane, Dr Abdelkader, Ph.D. "Graph of Exponential Functions." November 25, 2007.http://www.analyzemath.com/Graphing/GraphExponentialFunction.html

Khan, Salman. "Identifying Exponential Models."

http://www.khanacademy.org/video/identifying-exponential-models (accessed September 11, 2010).