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# PHP atanh() Function [ PHP Math Reference](#) ## Example Return the inverse hyperbolic tangent of different numbers: <?php echo(atanh(M_PI_4) . "
"); echo(atanh(0.50) . "
"); echo(atanh(-0.50) . "
"); echo(atanh(1) . "
"); echo(atanh(-1)); ?> [Run Example »](#) * * * ## Definition and Usage The atanh() function returns the inverse hyperbolic tangent of a number. * * * ## Syntax atanh(_number_); | Parameter | Description | | --- | --- | | _number_ | Required. Specifies a number. | ## Technical Details | Return Value: | The inverse hyperbolic tangent of _number_. | | :--- | | Return Type: | Float | | PHP Version: | 4.1+ | | PHP Changelog: | PHP 5.3: The function is now available on all platforms. | * * PHP Math Reference](#)