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# Complex.Cos Method

Visual Studio 2010

Returns the cosine of the specified complex number.

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

## Syntax

```'Declaration
Public Shared Function Cos ( _
value As Complex _
) As Complex
```

#### 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.

```
Imports System.Numerics

Module Example
Public Sub Main()
Dim values() As Complex = { New Complex(.5, 2),
New Complex(.5, -2),
New Complex(-.5, 2),
New Complex(-.3, -.8) }
For Each value As Complex In values
Console.WriteLine("Cos(ACos({0})) = {1}", value,
Complex.Cos(Complex.Acos(value)))
Next
End Sub
End Module
' 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.