atan

    (PHP 4, PHP 5, PHP 7, PHP 8)

    atan — Arc tangent

    Description

    atan(float $num): float

    Returns the arc tangent of num in radians. atan() is the inverse function of tan(), which means that $num == tan(atan($num)) for every value of num that is in the domain of atan().

    Parameters

    num

    The argument to process

    Return Values

    The arc tangent of num in radians.

    See Also

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    User Contributed Notes 1 note

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    9
    Anonymous
    10 years ago
    Contrary to the current description, it should hold y == tan(atan(y)) for ALL y.
    However, x == atan(tan(x)) only holds for those x which are in the range of atan, which are those x with -pi/2 < x < pi/2.

    Of course, those equalities are limited by precision. On my machine
    tan(atan(1000)) returns 1000.0000000001.
    atan(tan(0)) returns 0 (correct).
    atan(tan(M_PI)) returns -1.2246467991474E-16 instead of 0.
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