C++ Reference Manual

C++ Library Function <cmath>

C ++acos() Function Usage and Example

This function returns the inverse cosine value of the number (parameter) in radians form in<cmath>Header file definition.

[Math] cos-1++]

acos() Prototype [From C ++ 11Standard Start]

double acos(double x);
float acos(float x);
long double acos(long double x);
double acos(T x);　//as an integer

acos() parameter

the acos() function uses[-1,1]within the range of a single mandatory parameter. This is because the cosine value in1to-1of.

the range of the acos() return value

Assuming the parameter is in[-1,1]the range, then the acos() function returns a value within the range [0, π].

If the parameter is greater than1or less-1, then acos() returns NaN, which is not a number.

Example1: How does acos() work?

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
　　double x = 0.0, result;
　　result = acos(x);
　　cout << "acos(x) = " << result << " radians" << endl;
　　
　　cout << "acos(x) = " << result*180/3.1415　<< "degrees" << endl;
　　
　　return 0;
}

When the program is run, the output is:

acos(x) =　1.5708　radians
acos(x) =　90.0027　degrees

Example2: The acos() function with integer type

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
　　int x =　-1;
　　double result;
　　result = acos(x);
　　
　　cout << "acos(x) = " << result << " radians" << endl;
　　//　Convert the result to degrees
　　cout << "acos(x) = " << result*180/3.1415　<< " " degrees;
　　
　　return 0;
}

When the program is run, the output is:

acos(x) =　3.14159　radians
acos(x) =　180.005　degrees

　 C++ Library Function <cmath>