

Giúp e làm câu này với ạ
[tex]\left | \underset{MA}{\rightarrow} + \underset{2MB}{\rightarrow} + \underset{3MC}{\rightarrow} \right | = 2\left | \underset{MA}{\rightarrow} + \underset{MB}{\rightarrow} + \underset{MC}{\rightarrow}\right |[/tex]
[tex]\left | \underset{MA}{\rightarrow} + \underset{2MB}{\rightarrow} + \underset{3MC}{\rightarrow} \right | = 2\left | \underset{MA}{\rightarrow} + \underset{MB}{\rightarrow} + \underset{MC}{\rightarrow}\right |[/tex]