# GoLang – Find Inverse of Cosine – Acos() Function – Examples & Explanation

`Acos()` function can be used to find the inverse of a cosine in Go language. The inverse of a cosine is also known as the arc cosine.
The standard math library of Go programming language has `Acos()` function. The purpose of this function is to calculate arc cosine or the inverse of the cosine of any given numeric value in the range of `-1` and `1`.

## Syntax of `Acos()` Function in GoLang

The syntax of `Acos()` function in Go Language is:

Note: `float64` is a data type in go language which has IEEE-754 64-bit floating-point numbers.
A special case is:
`Acos(x) = NaN if x < -1 or x > 1`

## Parameters of `Acos()` Function in GoLang

`x` – Any Valid Input value (positive or negative within the range of `-1` and `1`). This parameter is required.
Note: If the `x` parameter is not a number, `Acos()` function will return an `error`.

## Return Value of `Acos()` Function in GoLang

`Acos()` function will return the arc cosine (inverse of cosine) in radians of the given input (`x` – parameters).

## GoLang `Acos()` Function Example

Output of GoLang `Acos()` function:
`3.141592653589793`

Note: The input value (`x` – parameter) should be in the range of (`-1` to `1`). Any other number will return `NaN`. But if your input is not a number (you enter character like: `a`, `!`, `Z`) then the compiler will surely give you an `error`.