Cho tam giác ABC. Tìm quỹ tích điểm M sao cho:
a.\(\left|\overrightarrow{MA}+\overrightarrow{MB}\right|\) = \(\left|\overrightarrow{MA}-\overrightarrow{MB}\right|\)
b. \(\left|\overrightarrow{MA}+\overrightarrow{MB}+\overrightarrow{MC}\right|=\dfrac{3}{2}\left|\overrightarrow{MA}+\overrightarrow{MB}\right|\)
c. \(\left|\overrightarrow{MA}+2\overrightarrow{MB}+\overrightarrow{MC}\right|\) = \(\left|\overrightarrow{MA}+\overrightarrow{MB}-2\overrightarrow{MC}\right|\)