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'\" t
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH acosh 3 2025-05-17 "Linux man-pages (unreleased)"
.SH NAME
acosh, acoshf, acoshl \- inverse hyperbolic cosine function
.SH LIBRARY
Math library
.RI ( libm ,\~ \-lm )
.SH SYNOPSIS
.nf
.B #include <math.h>
.P
.BI "double acosh(double " x );
.BI "float acoshf(float " x );
.BI "long double acoshl(long double " x );
.P
.fi
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR acosh ():
.nf
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| _XOPEN_SOURCE >= 500
.\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.P
.BR acoshf (),
.BR acoshl ():
.nf
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
These functions calculate the inverse hyperbolic cosine of
.IR x ;
that is the value whose hyperbolic cosine is
.IR x .
.SH RETURN VALUE
On success, these functions return the inverse hyperbolic cosine of
.IR x .
.P
If
.I x
is a NaN, a NaN is returned.
.P
If
.I x
is +1, +0 is returned.
.P
If
.I x
is positive infinity, positive infinity is returned.
.P
If
.I x
is less than 1,
a domain error occurs,
and the functions return a NaN.
.SH ERRORS
See
.BR math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
.P
The following errors can occur:
.TP
Domain error: \f[I]x\f[] is less than 1
.I errno
is set to
.BR EDOM .
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR acosh (),
.BR acoshf (),
.BR acoshl ()
T} Thread safety MT-Safe
.TE
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
C99, POSIX.1-2001.
.P
The variant returning
.I double
also conforms to
SVr4, 4.3BSD.
.SH SEE ALSO
.BR asinh (3),
.BR atanh (3),
.BR cacosh (3),
.BR cosh (3),
.BR sinh (3),
.BR tanh (3)
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