作业帮13 16 题
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13 16 题
13 16 题
13 16 题
13.
∠A = 90-60=30
∠B=90+15=105
∠C=180-∠A-∠B=45
16.
∵ OB、OC分别平分∠ABC和∠ACB
∴ ∠OBC=1/2∠ABC ∠OCB=1/2∠ACB
∵ ∠A+∠ABC+∠ACB = 180 ∠BOC+∠OBC+∠OCB=180
∴ ∠A = 180-∠ABC-∠ACB
∴ ∠BOC = 180-∠OBC-OCB=180-1/2∠ABC-1/2∠ACB=1/2(180-∠ABC-ACB)+90
=1/2∠A+90