(PHP 4 >= 4.1.0, PHP 5, PHP 7)
acosh — Inverse hyperbolic cosine
acosh ( float $arg ) : float
Returns the inverse hyperbolic cosine of arg, i.e. the value whose hyperbolic cosine is arg.
arg
The value to process
The inverse hyperbolic cosine of arg
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https://www.php.net/manual/en/function.acosh.php