If  $\left(\begin{array}{ccc}1& 1& x\end{array}\right)\left(\begin{array}{ccc}1& 1& 2\\ 0& 3& -1\\ 0& 2& 1\end{array}\right)\left(\begin{array}{c}1\\ x\\ 1\end{array}\right)=O$, then  $x=$

$\left(\begin{array}{ccc}1& 1& x\end{array}\right)\left(\begin{array}{ccc}1& 1& 2\\ 0& 3& -1\\ 0& 2& 1\end{array}\right)\left(\begin{array}{c}1\\ x\\ 1\end{array}\right)=O$

$\Rightarrow \left(\begin{array}{ccc}1+0+0& 1+3+2x& 2-1+x\end{array}\right)\left[\begin{array}{c}1\\ x\\ 1\end{array}\right]=O$

$\Rightarrow \left(\begin{array}{ccc}1& 4+2x& 1+x\end{array}\right)\left[\begin{array}{c}1\\ x\\ 1\end{array}\right]=O$

$\Rightarrow 1+x(4+2x)+1+x=0$

$\Rightarrow 1+4x+2x^2+1+x=0$

$\Rightarrow 2x^2+5x+2=0$

$\Rightarrow 2x^2+4x+x+2=0$

$\Rightarrow 2x(x+2)+1(x+2)=0$

$\Rightarrow (2x+1)(x+2)=0$

$x=-\frac{1}{2},-2$