# perldoc > sin

    sin EXPR
    sin     Returns the sine of EXPR (expressed in radians). If EXPR is
            omitted, returns sine of $_.

            For the inverse sine operation, you may use the
            "[Math::Trig::asin](https://www.chedong.com/phpMan.php/perldoc/Math%3A%3ATrig%3A%3Aasin/markdown)" function, or use this relation:

                sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) }