# cos() function for complex number in C++

The cos() function for a complex number is defined in the complex header file. This function is the complex version of the cos() function. This function is used to calculate the complex cosine of complex number z. This function returns the cos of the complex number z.

Syntax:

`cos (z);`

Parameter:

• z: This method takes a mandatory parameter z which represents the complex number.

Return value: This function returns the cos() of complex number z. Below programs illustrate the cos() function in C++:

Program 1:

## CPP

 `// C++ program to demonstrate` `// example of cos() function`   `#include ` `#include `   `using` `namespace` `std;`   `// driver program` `int` `main()` `{` `    ``complex<``double``> complexnumber(0.0, 1.0);`   `    ``// use of cos() function for complex number` `    ``cout << ``"The cos of "` `<< complexnumber << ``" is "` `         ``<< ``cos``(complexnumber) << endl;`   `    ``return` `0;` `}`

Output:

`The cos of (0,1) is (1.54308,-0)`

Time Complexity: O(1)
Auxiliary Space: O(1)

Program 2:

## CPP

 `// C++ program to demonstrate` `// example of cos() function.` `#include ` `#include ` `using` `namespace` `std;`   `// driver program` `int` `main()` `{` `    ``complex<``double``> complexnumber(1.0, 0.0);`   `    ``// use of cos() function for complex number` `    ``cout << ``"The cos of "` `<< complexnumber << ``" is "` `         ``<< ``cos``(complexnumber) << endl;`   `    ``return` `0;` `}`

Output:

`The cos of (1,0) is (0.540302,-0)`

Time Complexity: O(1)
Auxiliary Space: O(1)

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