Pronunciation: /ˈkoʊ saɪn/ Explain
Abbreviation: cos

Click on the blue points and drag them to change the figure.

Manipulative 1 - Cosine Created with GeoGebra.

In right triangle trigonometry, the Cosine is defined to be equal to the length of the side adjacent to the angle divided by the length of the hypotenuse.[1]

On the unit circle, cosine is the directed distance of a point on the unit circle from the y-axis. Click on the blue point in manipulative 1 and drag it to change the figure.

The inverse of the cosine function is the arccosine function. The arccosine function can be written as arccos() or cos^(-1)().


  1. Fine, Henry B., Ph. D.. Number-System of Algebra Treated Theoretically and Historically. 2nd edition. pp 28,47. D. C. Heath & Co., Boston, U.S.A.. 1907. Last Accessed 8/6/2018. Buy the book
  2. Hutton, Charles. A Course in Mathematics, Volume II. 4th edition. pp 2-3. G. & J. Robinson. 1804. Last Accessed 8/6/2018. Buy the book

More Information

  • McAdams, David E.. Secant. All Math Words Encyclopedia. Life is a Story Problem LLC. 6/27/2018.

Cite this article as:

McAdams, David E. Cosine. 6/25/2018. All Math Words Encyclopedia. Life is a Story Problem LLC.

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Revision History

6/25/2018: Removed broken links, updated license, implemented new markup, updated GeoGebra apps. (McAdams, David E.)
1/5/2010: Expanded "References". (McAdams, David E.)
12/19/2009: Added "References". (McAdams, David E.)
12/2/2008: Added reference to arccosine. (McAdams, David E.)
10/30/2008: Changed manipulative to GeoGebra. (McAdams, David E.)
4/30/2008: Initial version. (McAdams, David E.)

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