Câu hỏi 15

Ta có: \(\left\{ \begin{array}{l}\overrightarrow {AB}  = \left( { - 1; - 2;1} \right)\\\overrightarrow {AC}  = \left( {3;4; - 1} \right)\end{array} \right. \Rightarrow \overrightarrow n  = \left[ {\overrightarrow {AB} ;\overrightarrow {AC} } \right] = \left( { - 2;2;2} \right)\)

\( \Rightarrow {S_{\Delta ABC}} = \dfrac{1}{2}\left| {\overrightarrow n } \right| = \dfrac{1}{2}\sqrt {4 + 4 + 4}  = \sqrt 3 \).

Chọn C.