atan2 y, x
Returns the arctangent of
y/x in
the range -[pi] to [pi].
A quick way to get an approximate value of [pi] is to say:
$pi = atan2(1,1) * 4;
For the tangent operation, you may use the POSIX::tan()
function, or use the familiar relation:
sub tan { sin($_[0]) / cos($_[0]) }
