Periodic Functions: Sine and cosine are periodic functions, which means that sine and cosine graphs repeat themselves in patterns. You can graph sine and cosine functions by understanding their period and amplitude.

### What Are Periodic Trigonometric Functions?

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*ClassBrain Math Tutorials*, 2 March 2013, 11:19 UTC, <http://www.classbrainmath.com/periodic-trigonometric-functions/> [accessed 23 September 2018] - The Chicago Manual of Style
- Cynthia Kirkeby, “What Are Periodic Trigonometric Functions?.”
*ClassBrain Math Tutorials*, http://www.classbrainmath.com/periodic-trigonometric-functions/ [accessed September 23, 2018]. - CBE/CSE style
- Cynthia Kirkeby, What Are Periodic Trigonometric Functions? [Internet]. ClassBrain Math Tutorials; 2013 March 2, 11:19 UTC [cited 2018 Sep 23]. Available from: http://www.classbrainmath.com/periodic-trigonometric-functions/.
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- Cynthia Kirkeby, What Are Periodic Trigonometric Functions?. ClassBrain Math Tutorials. March 2, 2013, 11:19 UTC. Available at: http://www.classbrainmath.com/periodic-trigonometric-functions/. Accessed September 23, 2018.