(PHP 4, PHP 5, PHP 7)
atan — Arc tangent
atan ( float $arg ) : float
Returns the arc tangent of arg
in radians. atan() is the inverse function of tan(), which means that a==tan(atan(a))
for every value of a that is within atan()'s range.
arg
The argument to process
The arc tangent of arg
in radians.
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https://www.php.net/manual/en/function.atan.php