C++ Reference Manual

C++ Library Function <cmath>

C ++asin() Function Usage and Example

This function returns the arcsine of a number in radians form.<cmath>defined in the header file.

[Mathematics] sin-1x = asin(x) [C++];

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

double asin(double x);
float asin(float x);
long double asin(long double x);
double asin(T x);

asin() parameters

The asin() function uses[-1,1]is a single required parameter within the range.

This is because the sine value in1to-1is within the range.

The return value of asin()

Assuming the parameter is in [-1,1within the range, then the asin() function returns[-π/ 2, π/ 2]values within the range.

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

Example1How does asin() work?

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
　　double x = 0.25, result;
　　result = asin(x);
　　
　　cout << "asin(x) = " << result << " radians" << endl;
　　cout << "asin(x) = " << result*180/3.1415　<< "degrees" << endl;
　　
　　return 0;
}

When the program is run, the output is:

asin(x) = 0.25268　radians
asin(x) =　14.4779　degrees

Example2: The asin() function with integer type

#include <iostream>
#include <cmath>
#define PI　3.141592654
using namespace std;
int main()
{
　　int x =　1;
　　double result;
　　
　　result = asin(x);
　　
　　cout << "asin(x) = " << result << " radians" << endl;
　　//Convert the result to degrees
　　cout << "asin(x) = " << result*180/PI << " degrees";
　　
　　return 0;
}

When the program is run, the output is:

asin(x) =　1.5708　radians
asin(x) =　90 degrees

　 C++ Library Function <cmath>