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quyenlexuandao
2 năm trước
Cho tam giác ABC có góc A vuông, kẻ đường cao AH. Gọi E, F lần lượt là hình chiếu của H lên AB và AC. a) Chứng minh rằng tứ giác AEHF là hình chữ nhật. b) Chứng minh AE.AB = AF.AC. c) Đường thẳng đi qua A vuông góc với EF cắt BC tại I. Chứng minh I là trung điểm của BC. giúp câu c thôi
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