# ACOS

The ACOS function returns the arccosine, or inverse cosine, of a number. It is useful for finding the angle whose cosine is the specified number, especially in trigonometry and geometry.

## Syntax

=ACOS(`number`

)

`Number` | The cosine of the angle for which you want to find the arccosine. |

`Number` | The cosine of the angle for which you want to find the arccosine. |

## About ACOS

When you're dealing with angles and need to find the precise angle whose cosine matches a given number, the ACOS function in Excel comes to the rescue. It plays a key role in trigonometry and geometry, providing a straightforward method to determine the arccosine, or inverse cosine, of a specified number. This is particularly handy for various calculations involving angles and their corresponding trigonometric functions.

## Examples

If you want to find the angle whose cosine is 0.5, you can use the ACOS function as follows: =ACOS(0.5). This will return the value of the angle in radians.

## Questions

**What does the ACOS function return?**

The ACOS function returns the arccosine of the given number, which represents the angle in radians whose cosine equals the specified number.

**What is the allowable range for the input number in the ACOS function?**

The input number for the ACOS function must fall within the range of -1 to 1. If the input number is outside this range, the function will result in a #NUM! error.

## Related functions

['COS'

'COSH'

'ASIN'

'ATAN']