acos(3M)

NAME

     acos - arc cosine function

SYNOPSIS

     cc [ flag ... ] file ... -lm [ library ... ]
     #include <math.h>

     double acos(double x);

DESCRIPTION

     The acos() function computes the principal value of the  arc
     cosine of x. The value of x should be in the range [-1,1].

RETURN VALUES

     Upon successful completion, acos() returns the arc cosine of
     x,  in the range [0,pi] radians. If the value of x is not in
     the range [-1,1], and is not _Inf or NaN, either 0.0 or  NaN
     is returned and errno is set to EDOM.

     If x is NaN, NaN is returned. If x is _Inf,  either  0.0  is
     returned  and  errno  is set to EDOM, or NaN is returned and
     errno may be set to EDOM.

     For exceptional cases, matherr(3M) tabulates the  values  to
     be returned as dictated by Standards other than XPG4.

ERRORS

     The acos() function will fail if:

     EDOM  The value x is not _Inf or NaN and is not in the range
           [-1,1].

     The acos() function may fail if:

     EDOM  The value x is _Inf.

USAGE

     An application wishing to check for error situations  should
     set  errno  to 0 before calling acos(). If errno is non-zero
     on return, or the  value  NaN  is  returned,  an  error  has
     occurred.

ATTRIBUTES

     See attributes(5) for descriptions of the  following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | MT-Level                    | MT-Safe                     |
    |_____________________________|_____________________________|

SEE ALSO

     cos(3M), isnan(3M), matherr(3M), attributes(5), standards(5)