Cho tam giác ABC có AB bằng AC và BC bé hơn AB, gọi M là trung điểm của BC. a) Chứng minh: tam giác ABM bằng tam giác ACM. Từ đó suy ra AM là tia phân giác của góc BAC b) Trên cạnh AB lấy điểm D sao cho CB bằng CD. Kẻ tia phân giác của góc BCD, tia này cắt cạnh BD tại N. Chứng minh: CN vuông góc với BD c) Trên tia đối của tia CA lấy điểm E sao cho AD bằng CE. Chứng minh: góc BCE bằng góc ADC d) Chứng minh: BA bằng BE

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