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huuloi3976236
2 năm trước
Cho nửa đường tròn (O) đường kính AB. Vẽ tiếp tuyến Ax, By với nửa đường tròn. Lấy điểm E thuộc nửa đường tròn, qua E kẻ tiếp tuyến với đường tròn cắt Ax tại D và By tại C. Chứng minh: a) 4 điểm A,D,E,O cùng nằm trên 1 đường tròn b) AD+BC = DC c) AD.BC = OE² d) AC cắt BD tại F. Chứng minh EF vuông góc AB
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