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acos() function with example in C++

C++ acos() function: Here, we are going to learn about the acos() function with example of cmath header in C++ programming language?
Submitted by IncludeHelp, on April 28, 2019

C++ acos() function

acos() function is a library function of cmath header, it is used to find the principal value of the arc cosine of the given number, it accepts a number (x) and returns the principal value of the arc cosine of x in radians.

Note: Value (x) must be between -1 to +1, else it will return a domain error (nan).

Syntax

Syntax of acos() function:

acos(x);

Parameter(s)

x – is the value whose arc cosine to be calculated.

Return value

double – it returns double type value that is the principal value of the arc cosine of the given number x.

Sample Input and Output

Input:
float x = 0.65;
    
Function call:
acos(x);    
    
Output:
0.863212

Example

// C++ code to demonstrate the example of 
// acos() function

#include <iostream>
#include <cmath>
using namespace std;

// main() section
int main()
{
    float x;
    
    x = -1.0;
    cout<<"acos("<<x<<"): "<<acos(x)<<endl;

    x = -0.89;
    cout<<"acos("<<x<<"): "<<acos(x)<<endl;    

    x = 0.65;
    cout<<"acos("<<x<<"): "<<acos(x)<<endl;    

    x = 1;
    cout<<"acos("<<x<<"): "<<acos(x)<<endl;        
    
    return 0;
}

Output

acos(-1): 3.14159
acos(-0.89): 2.66814
acos(0.65): 0.863212
acos(1): 0

Example with domain error

If we provide the value out of the range (except -1 to +1), it returns nan.

// C++ code to demonstrate the example of 
// acos() function

#include <iostream>
#include <cmath>
using namespace std;

// main() section
int main()
{
    float x;

    x = -0.89;  //no error
    cout<<"acos("<<x<<"): "<<acos(x)<<endl;    

    x = 2.65;   //error
    cout<<"acos("<<x<<"): "<<acos(x)<<endl;    

    x = -1.25;  //error
    cout<<"acos("<<x<<"): "<<acos(x)<<endl;        
    
    return 0;
}

Output

acos(-0.89): 2.66814
acos(2.65): nan
acos(-1.25): nan

Reference: C++ acos() function