# ACOSH function

ACOSH returns the inverse hyperbolic cosine of a number.

## Syntax

ACOSH (`number`)

This
function returns the inverse hyperbolic cosine of `number`--that
is the number whose hyperbolic cosine is `number`. `number` must
be greater than or equal to 1.

`=ACOSH(1)` returns `0`.

`=ACOSH(COSH(4))` returns `4`.