Returns the arc cosine of its argument.

    Format

      #include  <math.h>

      double acos  (double x);

      float acosf  (float x); (Integrity servers, Alpha)

      long double acosl  (long double x); (Integrity servers, Alpha)

      double acosd  (double x); (Integrity servers, Alpha)

      float acosdf  (float x); (Integrity servers, Alpha)

      long double acosdl  (long double x);

                          (Integrity servers, Alpha)

1  –  Argument

 x

    A radian expressed as a real value in the domain [-1,1].

2  –  Description

    The acos functions compute the principal value of the arc cosine
    of x in the range [0,pi] radians for x in the domain [-1,1].

    The acosd functions compute the principal value of the arc cosine
    of x in the range [0,180] degrees for x in the domain [-1,1].

    For abs(x) > 1, the value of acos(x) is 0, and errno is set to
    EDOM.