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asin()                   Calculate Arc Sine

 #include   <math.h>

 double     asin(x);                     Arc sine (in radians)
 double     x;

    asin() returns the arc sine value of 'x' in radians.  The return
    value will be in the range -./2 to ./2.  'x' must be in the range
    -1.0 to 1.0.

    Returns:    The arc sine of 'x'.  If 'x' < -1.0 or 'x' > 1.0, then
                matherr() is called with a DOMAIN error, 'errno' (defined
                in <stdlib.h>) is set to EDOM (defined in <math.h>), a
                domain error message is printed to 'stderr', and 0.0 is
                returned.

      Notes:    Error handling can be modified by using the matherr()
                routine.

  -------------------------------- Example ---------------------------------

    The following statements continue printing the arc sines of the
    values in an array until a DOMAIN error occurs.

           #include <math.h>       /* for asin() and EDOM */
           #include <stdio.h>      /* for printf() */
           #include <stdlib.h>     /* for errno */

                                /* the value 3.141 will cause an error */
           double sines[6] = {0.707, 0.0, 1.0, -1.0, 3.141, -0.2};

           main()
           {
               double arc_sine;
               int i;

               errno = 0;
               for (i = 0;  !errno && i < 6;  i++) {
                   arc_sine = asin(sines[i]);
                   if (errno == EDOM) /* an error is also printed to stderr
           */
                       printf("DOMAIN error in asin()\n");
                   printf("arc sine of %f = %f radians\n", sines[i],
                          arc_sine);
               }
           }