acosh(3) Library Functions Manual acosh(3)

# NAME¶

acosh, acoshf, acoshl - inverse hyperbolic cosine function

# LIBRARY¶

Math library (libm, -lm)

# SYNOPSIS¶

`#include <math.h>`
```double acosh(double x);
float acoshf(float x);
long double acoshl(long double x);```

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

acosh():

```
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

|| _XOPEN_SOURCE >= 500

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE```

acoshf(), acoshl():

```
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE```

# DESCRIPTION¶

These functions calculate the inverse hyperbolic cosine of x; that is the value whose hyperbolic cosine is x.

# RETURN VALUE¶

On success, these functions return the inverse hyperbolic cosine of x.

If x is a NaN, a NaN is returned.

If x is +1, +0 is returned.

If x is positive infinity, positive infinity is returned.

If x is less than 1, a domain error occurs, and the functions return a NaN.

# 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:

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 acosh (), acoshf (), acoshl () Thread safety MT-Safe

# STANDARDS¶

C99, POSIX.1-2001, POSIX.1-2008.

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