Question

已知ABCD都是在⊙O上不同的点AB=BA=CD,∠BCD=130°求AD弦所对的圆周角

Answer 1

同弦长圆周角相等

∠BDA＝∠BCA＝∠BDC＝∠BAC＝∠CAD＝∠CBD

∠ABD＝∠ACD

∠BDA+∠BCA+∠BDC+∠BAC+∠CAD+∠CBD+∠ABD+∠ACB＝360°

6∠BCA+2∠ACD＝360°

∠BCA+∠ACD＝130°

∠BCA＝25°

∠ACD＝105°