# Domain

Pronunciation: /doʊˈmeɪn/ Explain

 Figure 1: Domain and range.

The domain of a function is all values that an independent variable can take. The domain of a function is all the input values of the function. If the domain of a function is not explicitly restricted, its domain is called the domain of definition, all points for which the function is defined. The domain of definition can also be called the natural domain. On a Cartesian graph, the domain is typically the horizontal axis.

In the function , the domain of definition is or unrestricted, meaning it can take on any value. However, given the real function , the domain of definition is or , since the square root of a negative number is undefined for the set of real numbers.

A function can also have a restricted domain. For example, take the function with the restriction . While negative numbers are defined for the function, they are not in the domain.

A subdomain is part of the domain of a funtion. For example, a subdomain can be 0 ≤ x < 5.

### References

1. McAdams, David E.. All Math Words Dictionary, domain. 2nd Classroom edition 20150108-4799968. pg 66. Life is a Story Problem LLC. January 8, 2015. Buy the book
2. Bettinger, Alvin K. and Englund, John A.. Algebra and Trigonometry. pp 53-54. www.archive.org. International Textbook Company. January 1963. Last Accessed 7/3/2018. http://www.archive.org/stream/algebraandtrigon033520mbp#page/n70/mode/1up/search/domain. Buy the book
3. Goldrei, D.C.. Classic Set Theory: For Guided Independent Study. pg 4. Chapman & Hall Mathematics. July 1 1996. Last Accessed 7/3/2018. Buy the book
4. Gilbert, Jimmie; and Gilbert Linda. Elements of Modern Algebra. 6th edition. pp 13-14. Thomson, Brooks/Cole. 2005. Last Accessed 7/3/2018. Buy the book

McAdams, David E. Domain. 12/21/2018. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/d/domain.html.

### Revision History

12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)