Some authors have called inverse hyperbolic functions "area functions" to realize the hyperbolic angles.

(See inverse hyperbolic functions.)

In mathematics, the inverse hyperbolic functions provide a hyperbolic angle corresponding to a given value of a hyperbolic function.

The formula for the corresponding rapidity (the Inverse hyperbolic functions of the velocity divided by the speed of light) is simpler:

The inverse hyperbolic functions are the area hyperbolic sine "arsinh" (also called "asinh" or sometimes "arcsinh") and so on.