thanks 
R0J0hound ! This is actually for a top-down space shooter.. I have a big heavy cruiser that catches up with the player (in a straight line making course corrections until the ship is in range). Once the Cruiser is in range, it slows down and uses it's 360 degree cannon to shoot at the player. Once the player is out of range the Cruiser needs to pursue. This is where the easing comes in.. If the Cruiser needs to rotate it looks horrible with lerp() because there is no easing into the rotation - it happens way too fast - and if I slow the rate down, the ship does WAY too big of a loop to catchup to the player. It looks fine easing out of the rotation.
I'm just trying to make the movement seem semi-realistic due to the size of the ship - with so much mass you'd probably see slow and small rotations.
so currently I'm doing:
anglelerp(self.Angle,angle(self.X,self.Y,Player_ship.X,player_ship.Y),0.005)
and instead I need:
anglecosp(self.Angle,angle(self.X,self.Y,Player_ship.X,player_ship.Y),0.005)
The one bug is if the course corrections(Cruiser ship rotation) are still happening when the target is in range. (because it's not supposed to rotate when the target is in range). The rotation suddenly stops - which kills the easing. But I've coded for that giving the ship some fake "aftertouch" which helps it looks like it'm slowing down to a natural speed. Even if it over shoots it doesn't matter since the ship has a gun with a 360 degree range - as long as it's headed in the direction of the player its fine.
thanks for the capx.. that looks perfect! it should work!