1、∠BOC=180°-(∠OBC+∠OCB)
=180°-1/2(∠ABC+∠ACB)
=180°-1/2(180°-∠A)
=180°-90°+1/2∠A
=90°+1/2∠A
2、∠BO2C=180°-(∠O2BC+∠O2CB)
=180°-2/3(∠ABC+∠ACB)
=180°-2/3(180°-∠A)
=180°-120°+2/3∠A
=60°+2/3∠A
3、∠BO1C=180°-(∠O1BC+∠O1CB)
=180°-1/n(∠ABC+∠ACB)
=180°-1/n(180°-∠A)
=180°(n-1)/n+1/n∠A
∠BOn-1C=180°/n+(n-1)/n∠A
∠BOiC=180°(n-i)/n+i/n∠A