Question

△ABCD中,AB＞AC,∠AEF=∠AFE,延∠长EF与BC的延长线交于G,求证1/2（∠ACB—∠B）

Answer 1

因为,∠ACB = ∠G+∠CFG = ∠G+∠AFE = ∠G+∠AEF = ∠G+(∠G+∠B) = 2∠G+∠B ,

所以,∠G = (1/2)(∠ACB-∠B) .