# C++ <complex> - acos() Function

The C++ <complex> acos() function returns the complex arc cosine of a complex number z. It is a function on complex plane, and has two branch cuts:

• Extends right from 1 along the real axis to ∞, continuous from below.
• Extends left from -1 along the real axis to -∞, continuous from above.

Mathematically, it can be expressed as: For any z, acos(z) = 𝜋 - acos(-z)

### Syntax

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

### Parameters

 `z` Specify the complex number.

### Return Value

Returns the complex arc cosine of z.

### Example:

The example below shows the usage of <complex> acos() function.

```#include <iostream>
#include <complex>
using namespace std;

int main (){
complex<double> z1 (2, 2);
complex<double> z2 (2, 0);
complex<double> z3 (0, 2);

//calculate the complex arc cosine
cout<<"acos(z1): "<<acos(z1)<<"\n";
cout<<"acos(z2): "<<acos(z2)<<"\n";
cout<<"acos(z3): "<<acos(z3)<<"\n";

return 0;
}
```

The output of the above code will be:

```acos(z1): (0.816547,-1.73432)
acos(z2): (0,-1.31696)
acos(z3): (1.5708,-1.44364)
```

❮ C++ <complex> Library

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