$${\mathtt{2}}{\mathtt{\,\times\,}}{{\mathtt{x}}}^{{\mathtt{2}}} = {\mathtt{18}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{x}} = -{\mathtt{3}}\\
{\mathtt{x}} = {\mathtt{3}}\\
\end{array} \right\}$$
$${\mathtt{2}}{\mathtt{\,\times\,}}{{\mathtt{x}}}^{{\mathtt{2}}} = {\mathtt{18}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{x}} = -{\mathtt{3}}\\
{\mathtt{x}} = {\mathtt{3}}\\
\end{array} \right\}$$