# Ruby – Find Arc Cosine – acos() Method – Examples & Explanation

`acos()` method can be used to find the arc cosine of the any given complex number in Ruby language.

## `acos()` Method in Ruby

`acos()` method exists in Standard CMath Library of Ruby. The purpose of this method is to provide perfect arc cosine for the given complex number.

## Syntax of the `acos()` Method in Ruby

Syntax of `acos()` method is:

```cmath.acos(x)
```

## Parameter of `acos()` Method in Ruby

 Parameter Description x Any valid complex number. This parameter is required.

Note: If the` x` parameter is not a number, `acos()` method will return an `error`.

## Return Value of `acos()`

`acos()` method will returns the arc cosine of the given numeric complex number.

## How to get the `acos()` Value of Given Numbers in Ruby?

``` #import CMath library
require 'cmath'
x = CMath.acos(1 + 1i)
puts x
```

Output

`0.9045568943023813-1.0612750619050357i`

## Ruby `acos()` Method Example 2

``` #import CMath library
require 'cmath'
x = CMath.acos(-1 + 1i)
puts x
```

Output

` 2.2370357592874117-1.0612750619050357i`

## Ruby – Various Ways to Get the `acos()` of Given Numbers Example 3

``` #import CMath library
require 'cmath'
x = CMath.acos(0 + 0i)
puts x
```

Output

` 1.5707963267948966+0.0i`

## Ruby `acos()` Method Example 4

``` #import CMath library
require 'cmath'
x = CMath.acos(-5 - 5i)
puts x
```

Output

` 2.3511949067802878+2.649196177806475i`

## Ruby `acos()` Method Example 4

``` #import CMath library
require 'cmath'
x = CMath.acos(-5)
puts x
```

Output

`3.141592653589793-2.2924316695611777i`

## Ruby `acos()` Method Example 4

``` #import CMath library
require 'cmath'
x = CMath.acos(0)
puts x
```

Output

`1.5707963267948966`