3.2.149 sin

sin EXPR

Sorry, there's nothing wicked about this operator. It merely returns the sine of EXPR (expressed in radians). If EXPR is omitted, it 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])) }