# .Acos()

The `Math.Acos()` method returns the absolute value of the inverse cosine of the argument, measured in radians. In other words, it returns the positive angle whose cosine is the specified number.

## Syntax

``````Math.Acos(x);
``````

The method takes one parameter `x` of the type `double`. It will return a positive value of type `double` except in the following cases:

• If `x` is less than -1, it will return `NaN` (not a number).
• If `x` is greater than 1, it will return `NaN`.
• If `x` is `NaN`, it will return `NaN`.

## Example

The following example prints the results of the `Math.Acos()` method for five different values.

```using System;
namespace MyMathExample{    public class Example    {        public static void Main(string[] args)        {            double a = Math.Acos(0.5);            double b = Math.Acos(1);            double c = Math.Acos(-2);            double d = Math.Acos(4);            double e = Math.Acos(0);
Console.WriteLine(a);            Console.WriteLine(b);            Console.WriteLine(c);            Console.WriteLine(d);            Console.WriteLine(e);        }    }}
```

This results in the following output:

```1.04719755119660NaNNaN1.5707963267949
```

## Codebyte Example

The example below uses `Math.Acos()` to calculate the arc cosine of `x`. The result is stored in the `result` variable.

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