(探索题)如图△ABC中,∠ABC,∠ACB的平分线相交于点O. (1)若∠ABC=40°,∠ACB=80°,求∠BOC; (2)你能找出∠A与∠BOC之间的数量关系吗?

问题描述:

(探索题)如图△ABC中,∠ABC,∠ACB的平分线相交于点O.

(1)若∠ABC=40°,∠ACB=80°,求∠BOC;
(2)你能找出∠A与∠BOC之间的数量关系吗?

(1)∠BOC=180°-

1
2
∠OBC-
1
2
∠OCB
=180°-
1
2
(∠OBC+∠OCB)
=180°-
1
2
(40°+80°)
=180°-
1
2
×120°
=120°;
(2)∠BOC=180°-
1
2
(∠ABC+∠ACB)
=180°-
1
2
(180°-∠A)
=90°+
1
2
∠A.