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chungloga123
2 năm trước
Cho tam giác ABC có ba góc đều nhọn nội tiếp đường tròn ( O;R). Các đường cao AD, BE và CF cắt nhau tại H. a) Chứng minh các tứ giác cdhe và bcef nội tiếp đường tròn b) Gọi I là trung điểm của BC. Lấy K là điểm đối xứng của H qua I. Chứng minh AK là đường lính của đường tròn (O;R) c) Chứng minh nếu tam giác abc có tanB.tanC=3 thì OH//BC Giải gấp giúp với ạ
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