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Related to arc cosine: Arctan, Inverse sine
arc cosine[′ärk ′kō‚sīn]
Also known as anticosine; inverse cosine.
For a number x, any angle whose cosine equals x.
For a number x, the angle between 0 radians and π radians whose cosine equals x ; it is the value at x of the inverse of the restriction of the cosine function to the interval between 0 and π.