atan2

atan2 Y, X

This function returns the arctangent of Y/X in the range -to A quick way to get an approximate value of 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]) }