做视频太麻烦了,再说我还没摄像头,还是文字说明吧.
∠ABC=2∠OBC ∠ACB=2∠OCB
∵∠ABC+∠ACB=180°-60°=120°
∴∠OBC+∠OCB=120°/2=60°
∴∠BOC=180°-60°=120°