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#### NAME

```       cacosh, cacoshf, cacoshl - complex arc hyperbolic cosine

```

#### SYNOPSIS

```       #include <complex.h>

double complex cacosh(double complex z);
float complex cacoshf(float complex z);
long double complex cacoshl(long double complex z);

```

#### DESCRIPTION

```       These  functions calculate the complex arc hyperbolic cosine of z.  If y = cacosh(z), then
z = ccosh(y).  The imaginary part of y is chosen in the interval [-pi,pi].  The real  part
of y is chosen nonnegative.

One has:

cacosh(z) = 2 * clog(csqrt((z + 1) / 2) + csqrt((z - 1) / 2))

```

#### VERSIONS

```       These functions first appeared in glibc in version 2.1.

```

#### ATTRIBUTES

```       For an explanation of the terms used in this section, see attributes(7).

┌───────────────────────────────┬───────────────┬─────────┐
│Interface                      │ Attribute     │ Value   │
├───────────────────────────────┼───────────────┼─────────┤
│cacosh(), cacoshf(), cacoshl() │ Thread safety │ MT-Safe │
└───────────────────────────────┴───────────────┴─────────┘
```

#### CONFORMINGTO

```       C99, POSIX.1-2001, POSIX.1-2008.

```

#### EXAMPLE

```       /* Link with "-lm" */

#include <complex.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>

int
main(int argc, char *argv[])
{
double complex z, c, f;

if (argc != 3) {
fprintf(stderr, "Usage: %s <real> <imag>\n", argv[0]);
exit(EXIT_FAILURE);
}

z = atof(argv[1]) + atof(argv[2]) * I;

c = cacosh(z);
printf("cacosh() = %6.3f %6.3f*i\n", creal(c), cimag(c));

f = 2 * clog(csqrt((z + 1)/2) + csqrt((z - 1)/2));
printf("formula  = %6.3f %6.3f*i\n", creal(f2), cimag(f2));

exit(EXIT_SUCCESS);
}

```

#### SEEALSO

```       acosh(3), cabs(3), ccosh(3), cimag(3), complex(7)

```

#### COLOPHON

```       This  page  is  part of release 5.02 of the Linux man-pages project.  A description of the