Tam giác ABC có trọng tâm G, độ dài các cạnh BC, CA, AB lần lượt là a, b, c. Khi đó ABC là tam giác đều nếu có điều kiện nào sau đây?

A.  a G A →   +   b G B →   +   c G C →   =   0 →

B.  a G A →   +   b G B →   -   c G C →   =   0 →

C.  a G A →   -   b G B →   +   c G C →   =   0 →

D.  - a G A →   +   b G B →   +   c G C →   =   0 →

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Everybody likes to watch TV and everybody has a favourite TV programme. I want to tell you about my favourite TV programme. I like to watch TV programme "Week of sports" very much, because I like sport. My favourite kind of sports is HOCKEY! I also like tennis and football. In this programme it is told about hockey, tennis. footbal and other kind of sports. That`s why I like it very much. It is told about all events of sports. "Week of sports"is very interesting and faseinating. I recommend to watch it. I have told you about my favourite programme. Now I want to know about your favourite TV programme. What TV programme do you like? Why do you like to watch it?

Nguồn : Ribi Nhock Ngốc