Question

A,B,C,D都是⊙O上不同的点,AB=BC=CD,∠BCD=130°,求AD弦所对的圆周角的度数

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°

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