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

Last Updated : 17 Aug, 2022

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

Syntax:

```template<class T> complex<T>
acos (const complex<T>& z );```

Parameter: This method accepts a mandatory parameter z which represents the complex number.

Return value: This function returns the arc cosine of complex number z.

Below programs illustrate the acos() function in C++:

Example 1:

## cpp

 `// C++ program to demonstrate` `// example of acos() function`   `#include& lt; bits / stdc++.h & gt;`   `using` `namespace` `std;`   `// driver program` `int` `main()` `{` `    ``complex& lt;` `    ``double``& gt;` `    ``complexnumber(-2.0, 0.0);`   `    ``// use of acos() function for complex number` `    ``cout& lt;` `    ``<` `    ``"` `    ``The ``acos` `of& quot;` `    ``<` `    ``<` `    ``complexnumber& lt;` `    ``<` `    ``"` `    ``is& quot;` `    ``<` `    ``<` `    ``acos``(complexnumber) & lt;` `    ``<` `    ``endl;`   `    ``return` `0;` `}`

Output:

`The acos of (-2,0) is (3.14159,-1.31696)`

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

Example 2:

## cpp

 `// c++ program to demonstrate` `// example of acos() function.`   `#include& lt; bits / stdc++.h & gt;` `using` `namespace` `std;`   `// driver program` `int` `main()` `{` `    ``complex& lt;` `    ``double``& gt;` `    ``complexnumber(-2.0, -0.0);`   `    ``// use of acos() function for complex number` `    ``cout& lt;` `    ``<` `    ``"` `    ``The ``acos` `of& quot;` `    ``<` `    ``<` `    ``complexnumber& lt;` `    ``<` `    ``"` `    ``is& quot;` `    ``<` `    ``<` `    ``acos``(complexnumber) & lt;` `    ``<` `    ``endl;`   `    ``return` `0;` `}`

Output:

`The acos of (-2,-0) is (3.14159,1.31696)`

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

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