# ACOS function: Description, Usage, Syntax, Examples and Explanation

## What is ACOS function in Excel?

ACOS function is one of the Math and Trig functions in Microsoft Excel that 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 in the range 0 (zero) to pi.

## Syntax of ACOS function

ACOS(number)

The ACOS function syntax has the following arguments:

**Number:**The cosine of the angle you want and must be from -1 to 1.

## ACOS formula explanation

If you want to convert the result from radians to degrees, multiply it by 180/PI() or use the DEGREES function.

## Example of ACOS function

Steps to follow:

1. Open a new Excel worksheet.

2. Copy data in the following table below and paste it in cell A1

Note: For formulas to show results, select them, press F2 key on your keyboard and then press Enter.

You can adjust the column widths to see all the data, if need be.

Formula |
Description |
Result |

=ACOS(-0.5) | Arccosine of -0.5 in radians, 2*pi/3 | 2.094395102 |

=ACOS(-0.5)*180/PI() | Arccosine of -0.5 in degrees | 120 |

=DEGREES(ACOS(-0.5)) | Arccosine of -0.5 in degrees | 120 |