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# Complex.Cos Method

Silverlight

Returns the cosine of the specified complex number.

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

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)))

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 Demo(System.Windows.Controls.TextBlock outputBlock)
{
Complex[] values = { new Complex(.5, 2),
new Complex(.5, -2),
new Complex(-.5, 2),
new Complex(-.3, -.8) };
foreach (Complex value in values)
outputBlock.Text += String.Format("Cos(ACos({0})) = {1}", value,
Complex.Cos(Complex.Acos(value))) + "\n";
}
}
// 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)

```

#### Silverlight

Supported in: 5, 4

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.