Pronunciation: /ɑɹkˈkoʊ.saɪn/ Explain
Abbreviations: acos, arccos

A right triangle. One of the angles that is not the right angle is labeled 'theta'. The side adjacent to theta is labeled 'adjacent'. The side opposite the right angle is labeled 'hypotenuse'. Underneath the figure is the equation 'cosin^(-1)(hypotenuse/adjacent) = theta'.
Figure 1: Arccosine

An arccosine is an angle whose cosine is a particular value. The arccosine is a trigonometric function. The arccosine is the functional inverse of the cosine function. If adjacent/hypotenuse = cosine(θ) then cosine-1(hypotenuse/adjacent) = θ. Arccosine is written arccosin or cos-1.

Definition: y = cos-1 x if and only if x = cos y.


  1. McAdams, David E.. All Math Words Dictionary, arccosine. 2nd Classroom edition 20150108-4799968. pg 18. Life is a Story Problem LLC. January 8, 2015. Buy the book

More Information

  • McAdams, David E.. Cosine. Life is a Story Problem LLC. 6/19/2018.

Cite this article as:

McAdams, David E. Arccosine. 4/11/2019. All Math Words Encyclopedia. Life is a Story Problem LLC.

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Revision History

4/11/2019: Changed equations and expressions to new format. (McAdams, David E.)
12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)
6/15/2018: Removed broken links, updated license, implemented new markup. (McAdams, David E.)
5/5/2011: Initial version. (McAdams, David E.)

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