# acos() Math Function In C++

acos() Math Function In C++ is a mathematical function that helps to find out the inverse cosine of a number.

The inverse cosine of a number in radian is computed with this function.

``acos(x) = cos -1x``

## Syntax:

Let’s say the number is x. The syntax would be as follows:

``````float acos(float x);
double acos(double x);
long double acos(long double x);
double acos(integral x);  ``````

## Parameter:

x: The value for which the arc cosine must be computed. It should fall between [-1,1].

## Return value:

### Example-1:

Let’s look at a basic case where x is higher than 1.

```#include <iostream>
#include<math.h>
using namespace std;
int main()
{
float degree=90;
float x=degree*3.14/180;
std::cout << "Value of cosine is :" <<cos(x)<< std::endl;
cout<<"Inverse of cosine is :"<<acos(x);
return 0;
}  ```

Output:

``````Value of cosine is :0.000796274
Inverse of cosine is :nan  ``````

In this case, the acos() function computes the inverse cosine of an integer when x is larger than 1.

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## Example-2:

Let’s look at a basic case where x is equal to zero.

```#include <iostream>
#include<math.h>
using namespace std;
int main()
{
float degree=0;
float x=degree*3.14/180;
std::cout << "Value of cosine is :" <<cos(x)<< std::endl;
cout<<"Inverse of cosine is :"<<acos(x);
return 0;
}  ```

Output:

``````Value of cosine is :1
Inverse of cosine is :1.5708 ``````

When the value of x is equal to zero, the acos() function computes the inverse cosine of a number.

## Example-3

Let’s have a look at a basic case where x is smaller than -1.

```#include <iostream>
#include<math.h>
using namespace std;
int main()
{
float degree= -60;
float x=degree*3.14/180;
std::cout << "Value of cosine is :" <<cos(x)<< std::endl;
cout<<"Inverse of cosine is :"<<acos(x);
return 0;
}  ```

Output:

``````Value of cosine is :0.50046
Inverse of cosine is :nan  ``````

In this case, the acos() function computes the inverse cosine of an integer when x is less than -1. 