Question

Cho ΔABC nhọn (AB<AC). Đường cao AD, BE, CF cắt nhau ở H.

a) Chứng mình AEHF nội tiếp.

b) Gọi O là trung điểm BC, tia CB và EF cắt nhau ở M. CMR: góc FAD = góc OFC và OC²=OD.OM

c) CMR: MH ⊥ AO.

Answer 1

 ta có đường cao cf.be 
suy ra cfa bằng 90
suy ra hfa bằng 90(1)
suy ra bea bằng 90 
ssusuy rrara hea bằng 90 (2)
ttutưtừtừ 11 vvavàvà 22 ssusuysuy rrara
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