acosh, acoshf : inverse hyperbolic cosine

Synopsis

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

acosh calculates the inverse hyperbolic cosine of x. acosh is defined as x must be a number greater than or equal to 1. acoshf is identical, other than taking and returning floats.### Returns

acosh and acoshf return the calculated value. If x less than 1, the return value is NaN and errno is set to EDOM. You can change the error-handling behavior with the non-ANSI matherr function.

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**Authoritative source**: BUSMASTER DITA help source `acosh.dita`, compiled into `BUSMASTER.CHM` with the application.