∫AB∨CD

∴AB∥CD∥EG

∴∠ABE=∠BEG

∠CDE =∠ degree

∠∠BED =∠BEG+∠DEG

That is ∠ Abe +∠ CDE = 120.

∵BF aliquot ∠ABE, DF aliquot ∠CDE

∴∠ 1=∠2= 1/2∠ABE

∠3=∠4= 1/2∠CDE

∴∠ 1+∠2= 1/2∠abe+ 1/2∠cde= 1/2(∠abe+∠cde)= 1/2* 120 = 60

∵∠ bed = 120, ∴∠BED (large) = 360- 120 = 240.

Similarly, the sum of the internal angles of the quadrangle BEDF is 360 degrees.

∴∠f=360-240-(∠ 1+∠2)= 120-60=60