Prototype: double asin(double a_sin);
Header File: math.h (C) or cmath (C++)
Explanation: Asin is used to find the arcsine of a number (give it a sin value and it will return the angle, in radians corresponding to that value). It must be passed an argument between -1 and 1.

//Example gives the angle corresponding to sine 1
#include <iostream>
#include <cmath>

using namespace std;

int main()
Other Functions