∵ BO,CO分别平分∠ABC,∠ACB,
∴∠OBC=1/2∠ABC,∠OCB=1/2∠ACB,
∴∠BOC=180°﹣﹙ 1/2 ∠ ABC ﹢ 1/2 ∠ ACB﹚
=180°﹣1/2﹙ ∠ ABC +∠ ACB﹚
=180°-1/2×﹙80°+40°﹚
=120°.
∴∠ ABC与∠ ACB的和的一半与∠BOC互补.
∵ BO,CO分别平分∠ABC,∠ACB,
∴∠OBC=1/2∠ABC,∠OCB=1/2∠ACB,
∴∠BOC=180°﹣﹙ 1/2 ∠ ABC ﹢ 1/2 ∠ ACB﹚
=180°﹣1/2﹙ ∠ ABC +∠ ACB﹚
=180°-1/2×﹙80°+40°﹚
=120°.
∴∠ ABC与∠ ACB的和的一半与∠BOC互补.