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maikhanhchi2003
2 năm trước
Bài 4: (3,5 điểm). Cho noi tiếp dưong tròn tâm O, đưong kinh AB sao cho AC< BC; E là một điểm thuộc đoạn BC (E khác B và C). Tia AF cất đường tròn (0) tại điểm thứ hai D. Kẻ EH vuông góc với AB tại H Chứng minh rằng: Tú giác ACEH nội tiếp b, Tia CH cắt (O) tại điểm thứ hai F. Chimg minh rằng EH / DF c, Chứng minh rằng đường tròn ogoại tiếp tam giác CHO đi qua điểm D d. Gọi I và K lần lrợt là hình chiếu vuông góc của điểm F trên các đường thắng CA và CB. Chứng minh rằng ba đường thằng AB, DF, IK cùng đi qua nmột điểm. ( vẽ hình hộ nhé)
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