# acosh, acoshf, acoshl

Calculates the inverse hyperbolic cosine.

## Syntax

``````double acosh( double x );
float acoshf( float x );
long double acoshl( long double x );
``````
``````float acosh( float x );  // C++ only
long double acosh( long double x );  // C++ only
``````

### Parameters

x
Floating-point value.

## Return Value

The acosh functions return the inverse hyberbolic cosine (arc hyperbolic cosine) of x. These functions are valid over the domain x ≥ 1. If x is less than 1, `errno` is set to `EDOM` and the result is a quiet NaN. If x is a quiet NaN, indefinite, or infinity, the same value is returned.

Input SEH Exception `_matherr` Exception
± QNAN, IND, INF none none
x < 1 none none

## Remarks

When you use C++, you can call overloads of acosh that take and return float or long double values. In a C program, acosh always takes and returns double.

## Requirements

acosh, acoshf, acoshl <math.h> <cmath>

For additional compatibility information, see Compatibility.

## Example

``````// crt_acosh.c
// Compile by using: cl /W4 crt_acosh.c
// This program displays the hyperbolic cosine of pi / 4
// and the arc hyperbolic cosine of the result.

#include <math.h>
#include <stdio.h>

int main( void )
{
double pi = 3.1415926535;
double x, y;

x = cosh( pi / 4 );
y = acosh( x );
printf( "cosh( %f ) = %f\n", pi/4, x );
printf( "acosh( %f ) = %f\n", x, y );
}
``````
``````cosh( 0.785398 ) = 1.324609
acosh( 1.324609 ) = 0.785398
``````