cho nửa đường tròn (O ) đường kính AB vẽ các tiếp tuyến Ax , By với nửa đường tròn cùng phía với AB . từ điểm M trên nửa đường tròn (M khác A, B) Vẽ tiếp tuyến với đường tròn cắt Ax và By lần lượt tại C , D a chứng minh tam giác COD vuông , b Chứng minh MC.MD = $MO^{2}$ c, cho biết OC=BA=2R .Tính AC và BD theo R AI GIÚP MÌNH VỚI , MÌNH CẦN GẤP Ạ

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