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phammaitrinh52
2 năm trước
Cho tam giác ABC có ba đường trung tuyến AD, BE, CF cắt nhau tại G. Chứng minh rằng: a) AD<\frac{AB+AC}{2} ; b) BE+CF>\frac{3}{2}BC ; c*) 3/4 (AB + BC + AC) < AD + BE + CF < AB + BC + AC .
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