19.tex

\left\lbrack \begin{array}{}
\dfrac{\partial {{x}}_{1}}{\partial {{y}}_{1}}  & \dfrac{\partial {{x}}_{2}}{\partial {{y}}_{1}}  \\
 ~ \\
\dfrac{\partial {{x}}_{1}}{\partial {{y}}_{2}}  & \dfrac{\partial {{x}}_{2}}{\partial {{y}}_{2}}  \\
\end{array}\right\rbrack \left(\begin{array}{}
1 & 2 \\
3 & 4 \\
\end{array}\right)\left\{ \begin{array}{}
1 & 2 \\
3 & 4 \\
\end{array}\right\} \left\mid \begin{array}{}
1 & 2 \\
3 & 4 \\
\end{array}\right\mid \left\parallel \begin{array}{}
1 & 2 \\
3 & 4 \\
\end{array}\right\parallel