NAME

       acos, acosf, acosl - arc cosine function

SYNOPSIS

       #include <math.h>

       double acos(double x);
       float acosf(float x);
       long double acosl(long double x);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       acosf(), acosl():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

       These functions calculate the arc cosine of x; that is the value whose cosine is x.

RETURN VALUE

       On  success, these functions return the arc cosine of x in radians; the return value is in
       the range [0, pi].

       If x is a NaN, a NaN is returned.

       If x is +1, +0 is returned.

       If x is positive infinity or negative infinity, a  domain  error  occurs,  and  a  NaN  is
       returned.

       If x is outside the range [-1, 1], a domain error occurs, and a NaN is returned.

ERRORS

       See  math_error(7)  for information on how to determine whether an error has occurred when
       calling these functions.

       The following errors can occur:

       Domain error: x is outside the range [-1, 1]
              errno is set to EDOM.  An invalid floating-point exception (FE_INVALID) is raised.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌─────────────────────────┬───────────────┬─────────┐
       │Interface                │ Attribute     │ Value   │
       ├─────────────────────────┼───────────────┼─────────┤
       │acos(), acosf(), acosl() │ Thread safety │ MT-Safe │
       └─────────────────────────┴───────────────┴─────────┘

CONFORMING TO

       C99, POSIX.1-2001, POSIX.1-2008.

       The variant returning double also conforms to SVr4, 4.3BSD, C89.

SEE ALSO

       asin(3), atan(3), atan2(3), cacos(3), cos(3), sin(3), tan(3)

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at https://www.kernel.org/doc/man-pages/.

                                            2017-09-15                                    ACOS(3)