题目内容
如图, AB 为⊙ O 的直径, CD 为弦, AB ⊥ CD ,如果∠BOC = 70
,那么∠A的度数为
A 70
C . 30
B . 35
D . 20
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A 70
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B
分析:利用垂径定理得到弧BC等于弧BD,然后利用同弧或等弧所对的圆周角是圆心角的2倍求得圆周角即可.
解答:解:∵AB为⊙O的直径,CD为弦,AB⊥CD,
∴弧BC=弧BD
∵∠BOC=70°,
∴∠A的度数35°.
故选B.
解答:解:∵AB为⊙O的直径,CD为弦,AB⊥CD,
∴弧BC=弧BD
∵∠BOC=70°,
∴∠A的度数35°.
故选B.
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