\(\overrightarrow{AB}=\left(1;0;-3\right);\overrightarrow{AC}=\left(-1;1;0\right)\)
\(\Rightarrow\left(ABC\right)\) có một vtpt là \(\overrightarrow{n_{\left(ABC\right)}}=\left[\overrightarrow{AB};\overrightarrow{AC}\right]=\left(3;3;1\right)\)
\(\Rightarrow\) pt mặt phẳng (ABC) có dạng:
\(3\left(x-3\right)+3\left(y+1\right)+1\left(z-2\right)=0\)
\(\Leftrightarrow3x+3y+z-8=0\)