ACOS function in Excel is a mathematical function used to calculate the arccosine (inverse cosine) of a given number. It is useful for finding the angle in radians whose cosine is equal to the specified number. This function can be helpful in trigonometry and geometry problems.

## Syntax

**ACOS(number)**

## Arguments

number | The value for which you want to find the arccosine. This must be between -1 and 1. |

## How to use

To use the ACOS function, follow these steps:

- Start with an Excel worksheet and select the cell where you want the result to appear.
- Enter the formula with the desired number as an argument:
`=ACOS(number)`

- Press Enter, and Excel will calculate the arccosine of the provided number.

### Examples

Let’s explore some examples to understand how the ACOS function works:

**Example 1:** Find the arccosine of 0.5.

1 |
=ACOS(0.5) |

The result is approximately 1.0472 radians, which is equivalent to 60 degrees.

**Example 2 (Optional):** You can also find the arccosine of negative numbers, but remember that the result will be in the range of 0 to π (pi) radians.

1 |
=ACOS(-0.8) |

The result is approximately 2.498 radians, which is about 143 degrees.

**Example 3 (Optional):** If you provide a number outside the valid range, you’ll get an error. For instance, attempting to find the arccosine of 2 or -2 would result in an error.

## Additional information

The ACOS function is part of a group of trigonometric functions in Excel, making it useful for various math and science applications. Remember that the input number must be within the range of -1 to 1, and the result is always in radians.

If you need the result in degrees, you can use the RADIANS function to convert it. The arccosine function can be particularly useful in solving problems involving angles, such as in physics or engineering calculations.