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thanhchungbg2001
2 năm trước
Cho tam giác abc có 3 góc nhọn nối tiếp trong ( O ; R ) . Các đường cao BE , CF cắt nhau tại H , cắt đường tròn ( O ; R ) lần lượt tại M và N a. Chứng minh bốn điểm B,F,E,C thuộc một đường tròn b. Chứng minh AE × AC = AF × AB c. Chứng minh MN song song với EF. D. Chứng minh MN trên AH bé hơn 2
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