The ACOS function in Excel calculates the arccosine (inverse of cosine) of a given number and returns the angle in radians between 0 and π. Arccosine is inverse of cosine.

ARCCOS(**b/c)= **θ

Arccosine of the adjacent side – b, divided by the hypotenuse – c equal to the angle θ.

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**Syntax of ACOS Function in Excel**

ACOS(number)

Where Argument number is a value between -1 and 1 which you need to calculate the arccosine.

**Example of ACOS Function in Excel**

**Formula**

- From Row number 2 to 5 ACOS is calculated in radians for value between -1 and 1 that is being passed as input to the ACOS Function.
- In row number 6, ACOS is calculated in degree for the value 0 which is 90 degree

**Note: **if you want the value of ACOS Function to be calculated in degrees, then convert it in degrees using DEGREES Function as shown in 6^{th} row.