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thoan81
2 năm trước
Cho tam giác ABC nhọn, AB < AC. Vẽ đường tròn (O) đường kính BC cắt hai cạnh AB và AC lần lượt tại E và D, BD cắt CE tại H, AH cắt BC tại F. a/ Chứng minh : AF vuông BC tại F và tứ giác giác BEHF nội tiếp. b/ Tia DE cắt đường thẳng BC tại S. Chứng minh: SE.SD = SB.SC. c/ Tia AH cắt (O) tại K (F nằm giữa A và K). Chứng minh : SK là tiếp tuyến của (O).
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