May 6, 1991 ACOSH 3

### NAME

acosh, acoshf - inverse hyperbolic cosine function

### LIBRARY

Math Library (libm, -lm)

### SYNOPSIS

```double` acosh(```double x`)
```float` acoshf(```float x`)

### DESCRIPTION

The acosh(``) and acoshf(``) functions compute the inverse hyperbolic cosine of the real argument x.

### RETURN VALUES

If x is less than one, acosh(```x`) and acoshf(```x`) return NaN and set the global variable errno to EDOM.

### SEE ALSO

asinh(3), atanh(3), exp(3), math(3)

### HISTORY

The acosh(``) function appeared in 4.3BSD.