∠DBC=2∠ABD,∠DCB=2∠ACB若∠BDC=α+2／3∠A求α

∠DBC=2∠ABD,∠DCB=2∠ACD,∠BDC=α+2/3∠A,∠A=180-∠ABC-∠ACB=180-1.5∠DBC-1.5∠DCB ∠BDC=180-∠DBC-∠DCB 又∠BDC=α+2/3∠A=α+2/3(180-1.5∠DBC-1.5∠DCB)=α+120-∠DBC-∠DCB 故α=60