ACOS(3) Linux Programmer's Manual ACOS(3)
**NAME**
acos - arc cosine function
**SYNOPSIS**
**#include** **<math.h>**
**double** **acos(double** *x***);**
**DESCRIPTION**
The **acos()** function calculates the arc cosine of *x*; that
is the value whose cosine is *x*. If *x* falls outside the
range -1 to 1, **acos()** fails and *errno* is set.
**RETURN** **VALUE**
The **acos()** function returns the arc cosine in radians and
the value is mathematically defined to be between 0 and PI
(inclusive).
**ERRORS**
**EDOM** *x* is out of range.
**CONFORMING** **TO**
SVID 3, POSIX, BSD 4.3, ISO 9899
**SEE** **ALSO**
**asin**(3), **atan**(3), **atan2**(3), **cos**(3), **sin**(3), **tan**(3)
June 8, 1993 1