证明:
∵∠DBC=1/2∠ABC
∠DCB=1/2∠ACB
∴∠BDC=180º-∠DBC-∠DCB
=180º-1/2∠ABC-1/2∠ACB
=180º-1/2(∠ABC+∠ACB)
=180º-1/2(180º-∠A)
=180º-90º+∠A
=90º+∠A
得证
证明:
∵∠DBC=1/2∠ABC
∠DCB=1/2∠ACB
∴∠BDC=180º-∠DBC-∠DCB
=180º-1/2∠ABC-1/2∠ACB
=180º-1/2(∠ABC+∠ACB)
=180º-1/2(180º-∠A)
=180º-90º+∠A
=90º+∠A
得证