If you only need to rotate around the Z axis then it is a simple 2D trig problem. The z co-ordinate is invariant as this is our rotational plane.

sub rotate {
    my ( $x,$y,$z,$angle ) = @_;
    $angle = deg2rad($angle);
    my $x_new = cos($angle)*$x - sin($angle)*$y;
    my $y_new = sin($angle)*$x + cos($angle)*$y;
  return $x_new, $y_new, $z;
}
sub deg2rad { return 3.14159265358979*$_[0]/180 };
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Here is a nice article with a pretty applet Update Corrected error noted by johnnywang