∴∠2= 1/2∠ebd∠ 1= 1/2∠fcd
∠∠F =∠ 1-∠2，∠E=∠FCD-∠EBD=2(∠ 1-∠2)
∴2∠F=2(∠ 1-∠2)=∠E
That is, ∠ f =1/2 ∠ e.
Similarly ∠ e =1/2 ∠ a.
∴∠F= 1/4∠A