How to use the Excel ACOS function

The ACOS function returns the arccosine, or inverse cosine, of a number. The arccosine is the angle whose cosine is number. The returned angle is given in radians between 0 and π.

Syntax: =ACOS(number)

The ACOS function syntax has the following arguments:

  • number: A number between -1 and 1. It is the cosine of the angle that you wish to find.

Example: Let’s look at some Excel ACOS function examples and explore how to use the ACOS function as a worksheet function in Microsoft Excel:

Syntax:  =ACOS(C2)


Based on the Excel spreadsheet above, the following ACOS examples would return:

Syntax: =ACOS(C3)
Result: 2.094395102

Syntax: =ACOS(C4)
Result: 2.278380764

Syntax: =ACOS(C5)
Result: 1.570796327

Syntax: =ACOS(C6)
Result: 0.86321189

Syntax: =ACOS(C7)
Result: 1.047197551

Syntax: =ACOS(C8)
Result: 0

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