SIMPLE SOLUTIONS

# ACOS, ACOSF, ACOSL - reference manual online

Arc cosine function.

Chapter
2015-04-19
```ACOS(3)                             Linux Programmer's Manual                             ACOS(3)

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);

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

acosf(), acosl():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99

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.