Trong không gian $Oxyz$, cho các điểm $A\left( 1;0;2...

$\left\{ \begin{aligned}
& \overrightarrow{BC}=\left( 2;0;-1 \right) \\
& \overrightarrow{BD}=\left( 0;-1;2 \right) \\
\end{aligned} \right.$$\Rightarrow \left[ \overrightarrow{BC},\overrightarrow{BD} \right]=\left( -1;-4;-2 \right)\left( BCD \right)\overrightarrow{n}=\left( -1;-4;-2 \right)dA\left( BCD \right)d\overrightarrow{n}=\left( -1;-4;-2 \right)A\left( 1;0;2 \right)\left\{ \begin{aligned}
& t=-1 \\
& t=-1 \\
& t=-1 \\
\end{aligned} \right.\Leftrightarrow t=-1A\left( BCD \right)\left\{ \begin{aligned}
& x=2+t \\
& y=4+4t \\
& z=4+2t \\
\end{aligned} \right.$.