acos()

Prototype: double acos(double a_cos);
Header File: math.h (C) or cmath (C++)
Explanation: Acos is used to find the arccosine of a number (give it a cosine 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 cosine .5
#include <iostream>
#include <cmath>

using namespace std;

int main()
{
  cout<<acos(.5);
}

Other Functions