For drawing a regular polygon of n side using rotation we can say 360 degree must be divisible by 360. Since we can draw a Hexagon because 360/6 = 60 degree.So we can draw a hexagon using 60 degree rotation(where result will be your exterior angle. So in this we can say 60 degree will be exterior angle.) Similarly we can draw a 12 - gon. because 360/12 = 30 degree.So we can draw a 12 gon using 30 degree rotation.