acosh, acoshf---inverse hyperbolic cosine Synopsis
#include <math.h> double acosh(double x); float acoshf(float x);
Description
acosh calculates the inverse hyperbolic cosine of x.
acosh is defined as
log(x + sqrt(x*x-1))
x must be a number greater than or equal to 1.
acoshf is identical, other than taking and returning floats.
Returns
acosh and acoshf return the calculated value. If x
less than 1, the return value is NaN and errno is set to EDOM.
You can change the error-handling behavior with the non-ANSI
matherr function.
Portability
Neither acosh nor acoshf are ANSI C. They are not recommended
for portable programs.
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