NAME

       acos, acosf, acosl - arc cosine function

LIBRARY

       Math library (libm, -lm)

SYNOPSIS

       #include <math.h>

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

   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 <= 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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       C99, POSIX.1-2001.

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

SEE ALSO

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