by Cho hình hộp $ABCD.{{A}_{1}}{{B}_{1}}{{C}_{1}}{{D}_{1}}$ với $M=C{{D}_{1}}\cap {{C}_{1}}D$. Khi đó:
C. $\overrightarrow{AM}=\frac{1}{2}\overrightarrow{AB}+\frac{1}{2}\overrightarrow{AD}+\frac{1}{2}\overrightarrow{A{{A}_{1}}}$
B.$\overrightarrow{AM}=\frac{1}{2}\overrightarrow{AB}+\overrightarrow{AD}+\frac{1}{2}\overrightarrow{A{{A}_{1}}}$
C. $\overrightarrow{AM}=\overrightarrow{AB}+\overrightarrow{AD}+\frac{1}{2}\overrightarrow{A{{A}_{1}}}$
D.$\overrightarrow{AM}=\frac{1}{2}\overrightarrow{AB}+\frac{1}{2}\overrightarrow{AD}+\overrightarrow{A{{A}_{1}}}$
Hướng dẫn
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