#include <math.h>
double asin(double x);
float asinf(float x);
asin() computes the principal value of the arc sine of x.
The arc sine sin^(-1)(x) of x in the range between -Pi/2 and Pi/2, if x is in the range -1 <= x <= 1. If x is not in this range, the function returns NAN and sets errno to EDOM.