Variables are used throughout Algebra, Geometry, and Calculus. They are the basic building blocks. Variables are therefore very important to understand.

A variable is a symbol, such as x, that is used to describe an unknown number. In functions variables often represent not one number, but many different numbers. Understanding variables is essential for you to understanding problems that will need to be graphed.

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- Cynthia Kirkeby, “What Are Variables?.”
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*ClassBrain Math Tutorials*, 2 March 2013, 10:46 UTC, <http://www.classbrainmath.com/introduction-to-equations-defining-variables/> [accessed 25 March 2017] - The Chicago Manual of Style
- Cynthia Kirkeby, “What Are Variables?.”
*ClassBrain Math Tutorials*, http://www.classbrainmath.com/introduction-to-equations-defining-variables/ [accessed March 25, 2017]. - CBE/CSE style
- Cynthia Kirkeby, What Are Variables? [Internet]. ClassBrain Math Tutorials; 2013 March 2, 10:46 UTC [cited 2017 Mar 25]. Available from: http://www.classbrainmath.com/introduction-to-equations-defining-variables/.
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- Cynthia Kirkeby, What Are Variables?. ClassBrain Math Tutorials. March 2, 2013, 10:46 UTC. Available at: http://www.classbrainmath.com/introduction-to-equations-defining-variables/. Accessed March 25, 2017.