arc_sine
This function returns the principal value of the arc sine of x, expressed in radians.
double arc_sine(double x)
Parameters:
x
The number to calculate between -1 and 1.
Return value:
Arc sine of x, in the interval [-pi/2,+pi/2] radians. If x is out of the valid range, this function will return 0.
Remarks:
In trigonometrics, arc sine is the inverse operation of sine.
Example:

    void main()
    {
    alert("arc_sine test", "Arc sine of -1 is "+arc_sine(-1)+".");
    alert("arc_sine test", "Arc sine of 0 is "+arc_sine(0)+".");
    alert("arc_sine test", "Arc sine of 1 is "+arc_sine(1)+".");
    }