# Complex.Cos Method

.NET Framework 4

Returns the cosine of the specified complex number.

Namespace:  System.Numerics
Assembly:  System.Numerics (in System.Numerics.dll)

## Syntax

```public static Complex Cos(
Complex value
)
```

#### Parameters

value
Type: System.Numerics.Complex
A complex number.

#### Return Value

Type: System.Numerics.Complex
The cosine of value.

## Remarks

The Cos method for complex numbers corresponds to the Math.Cos method for real numbers.

The Cos method uses the following formula to calculate the cosine of the complex number a + bi:

(Cos(a) * Cosh(b), -(Sin(a) * Sinh(b)))

## Examples

The following example illustrates the Acos method. It shows that passing the value returned by the Acos method to the Cos method returns the original Complex value.

```
using System;
using System.Numerics;

public class Example
{
public static void Main()
{
Complex[] values = { new Complex(.5, 2),
new Complex(.5, -2),
new Complex(-.5, 2),
new Complex(-.3, -.8) };
foreach (Complex value in values)
Console.WriteLine("Cos(ACos({0})) = {1}", value,
Complex.Cos(Complex.Acos(value)));
}
}
// The example displays the following output:
//       Cos(ACos((0.5, 2))) = (0.5, 2)
//       Cos(ACos((0.5, -2))) = (0.5, -2)
//       Cos(ACos((-0.5, 2))) = (-0.5, 2)
//       Cos(ACos((-0.3, -0.8))) = (-0.3, -0.8)

```

Supported in: 4

Supported in: 4

## Platforms

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.