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CACOSH(3) Library Functions Manual CACOSH(3)

cacosh, cacoshf, cacoshl
complex inverse hyperbolic cosine

#include <complex.h>
double complex
cacosh(double complex z);
float complex
cacoshf(float complex z);
long double complex
cacoshl(long double complex z);

The cacosh(), cacoshf() and cacoshl() functions compute the complex inverse hyperbolic cosine of z.
For all complex floating-point numbers z,
cacosh(z) = i acos(z).

The cacosh(), cacoshf() and cacoshl() functions return the complex inverse hyperbolic cosine of z with imaginary part in the interval [-Pi, Pi], and non-negative real part.

casinh(3), catanh(3)

The cacosh(), cacoshf() and cacoshl() functions conform to ISO/IEC 9899:1999 (“ISO C99”).
June 5, 2013 OpenBSD-current