∴∠AEF=∠B+∠G (one outer angle of a triangle is equal to the sum of two non-adjacent inner angles)
∫∠ACB is the outer corner of △FCG (known).
∴∠ACB=∠CFG+∠G (one outer angle of a triangle is equal to the sum of two non-adjacent inner angles)
∠∠CFG =∠AFE (definition of vertex angle)
∠∠AEF =∠AFE (known)
∴∠CFG =∞∠AFE =∞∠AEF (equivalent substitution)
∴∠ACB=∠AEF+∠G (equivalent substitution)
∠∠AEF =∠b+∠G (the outer angle of a triangle is equal to the sum of two non-adjacent inner angles)
∴∠ACB=∠B+∠G+∠G (equivalent substitution)
2∠G=∠ACB-∠B
That is, ∠G= 1/2(∠ACB-∠B).
It is not easy to type so many words. Give me the best answer.