If ABCDEF be a regular hexagon and ¯¯¯¯¯¯¯¯AB=¯¯¯a, ¯¯¯¯¯¯¯¯BC=¯¯b, ¯¯¯¯¯¯¯¯¯CD=¯¯c then ¯¯¯¯¯¯¯¯AE is equal to