第1个回答 2020-06-27
抄错了吧?是∠BEC才能算
(1)∠ACD=180-∠ACB
CE平分∠ACD,所以∠ACE=(180-∠ACB)/2=90-∠ACB/2
∠ECB=∠ACE+∠ACB=90-∠ACB/2+∠ACB=90+∠ACB/2
BE平分∠ABC,∠EBC=∠ABC/2
∠BEC=180-(∠EBC+∠ECB)
=180-(∠ABC/2+90+∠ACB/2)
=180-90-(∠ABC+∠ACB)/2
=90-(∠ABC+∠ACB)/2
因为∠ABC+∠ACB=180-∠A
所以∠BEC=90-(180-∠A)/2=90-90+∠A/2=∠A/2
∠A=80,所以∠BEC=40
(2)∠BCE=∠A/2=a/2