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1,
Ta có: $\overrightarrow{AB}(0; 1; 0), \overrightarrow{AC}(0; 0; 1); \overrightarrow{AD}(1; 1; 0)$, suy ra:
$[\overrightarrow{AB}. \overrightarrow{AC}].\overrightarrow{AD}=(1; 0; 0)(1;1;0)=1\neq 0$
$\Rightarrow \overrightarrow{AB}, \overrightarrow{AC}; \overrightarrow{AD} $ không đồng phẳng
$\Leftrightarrow $ A, B, C, D không đồng phẳng
Ta có: $V_{ABCD}=\frac{1}{6}|[\overrightarrow{AB}. \overrightarrow{AC}].\overrightarrow{AD}|=\frac{1}{6} $
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