## Summary

The ACOS function returns the inverse cosine of a number. The function is the inverse of COS and expects input in the range from -1 to 1.

## Purpose

Get the inverse cosine of a value, in radians.

## Syntax

``=ACOS(number)``
• number - The value to get the inverse cosine of. The number must be between -1 and 1 inclusive.

## How to use

The ACOS function returns the inverse cosine of a value. Input to the arc-cosine function must be between -1 and 1, inclusive. Geometrically, given the ratio of a triangle's adjacent side over its hypotenuse, the function returns the angle of the triangle. For example, given a ratio of 0.5 the function returns the angle of 1.047 radians.

``````=ACOS(0.5) // Returns 1.047 radians
``````

### Convert Result to Degrees

To convert the result from radians to degrees, multiply the result by 180/PI() or use the DEGREES function. For example, the convert the result of ACOS(0.5) to degrees, you can use either formula below:

``````=ACOS(0.5)*180/PI() // Returns 60 degrees
=DEGREES(ACOS(0.5)) // Returns 60 degrees
``````

### Explanation

The graph of ACOS visualizes the output of the function in the range from -1 to 1. ACOS is the inverse of the COS function. However, because COS is a periodic function, the output of ACOS is limited to the range from 0 to π.

Graph courtesy of wumbo.net.

Author

### Dave Bruns

Hi - I'm Dave Bruns, and I run Exceljet with my wife, Lisa. Our goal is to help you work faster in Excel. We create short videos, and clear examples of formulas, functions, pivot tables, conditional formatting, and charts.