# c Programming/C Reference/complex.h/casinh

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`casinh`

is one of the Standard C library functions in the complex.h header file. It is used to calculate the complex and inverse hyperbolic sine of given angle or number. Just like sine operator has inverse as sin inverse, hyperbolic sine of complex number has this as an inverse function.

The prototype of this function is:

```
double complex casinh(double complex x);
```

if casinh(x) = y, then x = csinh(y). It can be also evaluated as: casinh(x) = clog(x+csqrt(x*x+1))

## return value[edit]

This function returns complex arc hyperbolic sine,in the range mathematically unbounded along real axis and in the interval along imaginary axis.

## compatibility[edit]

Win32, C99 7.3.6.2