# atanh(3M)

```

```

## NAME

```     acosh, asinh, atanh - inverse hyperbolic functions

```

## SYNOPSIS

```     cc [ flag ... ] file ... -lm [ library ... ]
#include <math.h>

double acosh(double x);

double asinh(double x);

double atanh(double x);

```

## DESCRIPTION

```     The acosh(),  asinh()  and  atanh()  functions  compute  the
inverse  hyperbolic cosine, sine, and tangent of their argu-
ment, respectively.

```

## RETURN VALUES

```     The  acosh(),  asinh()  and  atanh()  functions  return  the
inverse  hyperbolic cosine, sine, and tangent of their argu-
ment, respectively.

The acosh() function returns NaN and sets errno to EDOM when
its argument is less than 1.0.

The atanh() function returns NaN and sets errno to EDOM when
its argument has absolute value greater than 1.0.

The atanh() function returns _Inf and sets errno  to  ERANGE
when its argument is _1.0.

If x is NaN, the  asinh(),  acosh()  and  atanh()  functions
return NaN.

For exceptional cases, matherr(3M) tabulates the  values  to
be returned as dictated by Standards other than XPG4.

```

## ERRORS

```     The acosh() function will fail if:

EDOM  The x argument is less than 1.0.

The atanh() function will fail if:

EDOM  The x argument has an absolute value greater than 1.0.

ERANGE
The x argument has an absolute value equal to 1.0

```

## ATTRIBUTES

```
See attributes(5) for descriptions of the  following  attri-
butes:

____________________________________________________________
|       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
|_____________________________|_____________________________|
| MT-Level                    | MT-Safe                     |
|_____________________________|_____________________________|

```

```     cosh(3M), matherr(3M),  sinh(3M),  tanh(3M),  attributes(5),