atan2

atan2 
y
, 
x

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]) }