cos
See the current Perl documentation for cos.
Here is our local, out-dated (pre-5.6) version:
cos - cosine function
cos EXPR
Returns the cosine of
EXPR (expressed in radians). If
EXPR is omitted, takes cosine of
$_.
For the inverse cosine operation, you may use the POSIX::acos()
function, or use this relation:
sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }