# Cosine

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.[2]

On the unit circle, cosine is the directed distance of a point on the unit circle from the y-axis.

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

### References

1. McAdams, David E.. All Math Words Dictionary, cosine. 2nd Classroom edition 20150108-4799968. pg 49. Life is a Story Problem LLC. January 8, 2015. Buy the book
2. Fine, Henry B., Ph. D.. Number-System of Algebra Treated Theoretically and Historically. 2nd edition. pp 28,47. www.archive.org. D. C. Heath & Co., Boston, U.S.A.. 1907. Last Accessed 6/25/2018. http://www.archive.org/stream/thenumbersystemo17920gut/17920-pdf#page/n37/mode/1up/search/cosine. Buy the book
3. Hutton, Charles. A Course in Mathematics, Volume II. 4th edition. pp 2-3. www.archive.org. G. & J. Robinson. 1804. Last Accessed 6/25/2018. http://www.archive.org/stream/courseofmathemat02huttrich#page/2/mode/1up/search/cosecant. Buy the book

• McAdams, David E.. Secant. allmathwords.org. All Math Words Encyclopedia. Life is a Story Problem LLC. 6/27/2018. http://www.allmathwords.org/en/s/secant.html.

McAdams, David E. Cosine. 4/16/2019. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/c/cosine.html.

### Revision History

4/16/2019: Updated equations and expressions to new format. (McAdams, David E.)
12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)