Linux Programmer’s Manual
acosh, acoshf, acoshl − inverse hyperbolic cosine function
double acosh(double x);
float acoshf(float x);
long double acoshl(long double x);
Link with −lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
acosh(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; or
acoshf(), acoshl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
_ISOC99_SOURCE; or cc -std=c99
The acosh() function calculates the inverse hyperbolic cosine of x; that is the value whose hyperbolic
cosine is x.
On success, these functions return the inverse hyperbolic cosine of x.
If x is a NaN, a NaN is returned.
If x is +1, +0 is returned.
If x is positive infinity, positive infinity is returned.
If x is less than 1, a domain error occurs, and the functions return a NaN.
See math_error(7) for information on how to determine whether an error has occurred when calling these
The following errors can occur:
Domain error: x is less than 1
errno is set to EDOM. An inv alid floating-point exception (FE_INVALID) is raised.
C99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD, C89.
asinh(3), atanh(3), cacosh(3), cosh(3), sinh(3), tanh(3)
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