In the figure, ∠ABC=80∘,∠ABC is bisected and the resultant angles are bisected again.
Then, ∠ABD+∠ABF−(∠EBF+∠DBC+∠FBC) is equal to:
0∘
∠ABD=40∘
∠ABF=60∘
∠EBF=40∘
∠DBC=40∘
∠FBC=20∘
So, ∠ABD+∠ABF−(∠EBF+∠DBC+∠FBC)=40∘+60∘−(40∘+40∘+20∘)=100∘−100∘=0∘