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ątÿĈ要确定点与圆的位置关系,主要确定点与圆心的距离与半径的大小关系;则dĚr 时,点在圆外;
当děr 时,点在圆上;当dĜr 时,点在圆内.
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故选C"
ą*ĞĈ本题考查了对点与圆的位置关系的判断.关键要记住若半径为r,点到圆心的距离为d,则有:当
dĚr 时,点在圆外;当děr 时,点在圆上,当dĜr 时,点在圆内.
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∴∠𝐸𝑂𝐷= ∠𝐷= 20°.
∴∠𝑂𝐸𝐶= 2∠𝐷= 40°L
∴∠𝑂𝐶𝐸= ∠𝑂𝐸𝐶= 40°L
∴∠𝐶𝑂𝐵= ∠𝐷+∠𝑂𝐶𝐸= 20° + 40° = 60°.
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