题目内容
(本题6分)已知:如右图,AB是⊙O的弦,⊙O的半径为5,OC⊥AB于点D , 交⊙O于点C,且AB = 8,求CD的长.
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解:连接OA, …………(1分)
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∵ OC⊥AB于点D , AB = 8,∴ AD=
=4, …(3分)
∵ Rt△AOD中,OA=5,AD=4,
∴OD=
=3, ……(5分)
∴CD=OC-OD="5-3=2 " …………(6分)
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∵ OC⊥AB于点D , AB = 8,∴ AD=

∵ Rt△AOD中,OA=5,AD=4,
∴OD=

∴CD=OC-OD="5-3=2 " …………(6分)
略
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