所求=180°-∠B-∠C =180°-(∠B +∠C) =180°-(180°-∠A) =180°-(180°- 80°) =180°- 50° =130°
角bic=180-1/2(角b+角c)
=180-1/2(180-角a)
=180-1/2*100
=180-50
=130
△ABC中,若∠A=80°,且∠B和∠C的角平分線相交於I點,則∠BIC= (..-阿摩線上測驗