

Cho hình chóp S.ABCD. Tìm điểm O sao cho
[tex]\inline \underset{OA}{\rightarrow} +\underset{OB}{\rightarrow} +\underset{OC}{\rightarrow} +\underset{OD}{\rightarrow} +\underset{OS}{\rightarrow} =\underset{0}{\rightarrow}[/tex]
[tex]\inline \underset{OA}{\rightarrow} +\underset{OB}{\rightarrow} +\underset{OC}{\rightarrow} +\underset{OD}{\rightarrow} +\underset{OS}{\rightarrow} =\underset{0}{\rightarrow}[/tex]