@c ----------------------------------------------------------------------
@node acos, math
@subheading Syntax

@example
#include <math.h>

double acos(double x);
@end example

@subheading Description

This function returns the angle in the range @code{[0..Pi]} radians
whose cosine is @var{x}.  If the absolute value of @var{x} is greater
than 1, a domain error occurs, and @code{errno} is set to @code{EDOM}.

@subheading Return Value

The arc cosine, in radians, of @var{x}.  If the absolute value of
@var{x} is greater than 1, the function returns a @code{NaN}.

@subheading Portability

@portability ansi, posix