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# cos

Visual Studio 2015

Returns the cosine of a complex number.

```template<class Type>
complex<Type> cos(
const complex<Type>& _ComplexNum
);
```

## Parameters

_ComplexNum

The complex number whose cosine is being determined.

## Return Value

The complex number that is the cosine of the input complex number.

## Remarks

Identities defining the complex cosines:

cos (z) = (1/2)*( exp (iz) + exp (-iz) )

cos (z) = cos (a + bi) = cos (a) cosh (b) - isin (a) sinh (b)

## Example

```// complex_cos.cpp
// compile with: /EHsc
#include <vector>
#include <complex>
#include <iostream>

int main( )
{
using namespace std;
double pi = 3.14159265359;
complex <double> c1 ( 3.0 , 4.0 );
cout << "Complex number c1 = " << c1 << endl;

// Values of cosine of a complex number c1
complex <double> c2 = cos ( c1 );
cout << "Complex number c2 = cos ( c1 ) = " << c2 << endl;
double absc2 = abs ( c2 );
double argc2 = arg ( c2 );
cout << "The modulus of c2 is: " << absc2 << endl;
cout << "The argument of c2 is: "<< argc2 << " radians, which is "
<< argc2 * 180 / pi << " degrees." << endl << endl;

// Cosines of the standard angles in the first
// two quadrants of the complex plane
vector <complex <double> > v1;
vector <complex <double> >::iterator Iter1;
complex <double> vc1  ( polar (1.0, pi / 6) );
v1.push_back( cos ( vc1 ) );
complex <double> vc2  ( polar (1.0, pi / 3) );
v1.push_back( cos ( vc2 ) );
complex <double> vc3  ( polar (1.0, pi / 2) );
v1.push_back( cos ( vc3) );
complex <double> vc4  ( polar (1.0, 2 * pi / 3) );
v1.push_back( cos ( vc4 ) );
complex <double> vc5  ( polar (1.0, 5 * pi / 6) );
v1.push_back( cos ( vc5 ) );
complex <double> vc6  ( polar (1.0,  pi ) );
v1.push_back( cos ( vc6 ) );

cout << "The complex components cos (vci), where abs (vci) = 1"
<< "\n& arg (vci) = i * pi / 6 of the vector v1 are:\n" ;
for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
cout << *Iter1 << endl;
}
```
```Complex number c1 = (3,4)
Complex number c2 = cos ( c1 ) = (-27.0349,-3.85115)
The modulus of c2 is: 27.3079
The argument of c2 is: -3.00009 radians, which is -171.893 degrees.

The complex components cos (vci), where abs (vci) = 1
& arg (vci) = i * pi / 6 of the vector v1 are:
(0.730543,-0.39695)
(1.22777,-0.469075)
(1.54308,1.21529e-013)
(1.22777,0.469075)
(0.730543,0.39695)
(0.540302,-1.74036e-013)```