Cho đường tròn tâm O, bán kính R đường kính AC. K là điểm nằm ngoài đường tròn. Từ K kẻ 2 tiếp tuyến KA và KB ( A ; B là các tiếp điểm ). tiếp tuyến tại C cắt của ( O;R) cắt AB tại E. 1. Cm : AK.BE=OA.BC 2, CM :tam giác KBC đồng dạng với tam giác OBE 3, CM : CK vuông góc với OE Làm giúp mình bài này với

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