N
nightlady


Cho tam giac ABC. Ke phan giac trong BD, CE cua goc B, goc C. Dung M doi xung voi A qua CE. Dung N doi xung voi A qua BD. Goi O la giao diem BD, CE. Ke OH vuong goc BC tai H. C/m M, N doi xung nhau qua OH.
Ai giai duoc minh se thanks

Ai giai duoc minh se thanks
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