Calculates the hyperbolic arc cosine of a floating-point number.
long double acoshl(long double d);
d Floating-point number for which hyperbolic arc cosine is to be computed
Normal: Hyperbolic arc cosine of d
Abnormal: Domain error: Returns NaN.
Error conditions: A domain error occurs when d is smaller than 1.0.
The acosh function returns the hyperbolic arc cosine in the range [0, +∞].