See the current Perl documentation for sin.

Here is our local, out-dated (pre-5.6) version:

sin - return the sin of a number

sin EXPR


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

For the inverse sine operation, you may use the POSIX::asin() function, or use this relation:

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