>>102
\begin{equation*}
\begin{pmatrix}
a_{11} &a_{12} \\
a_{21} &a_{22}+b_{12}
\end{pmatrix}, \qquad
\begin{pmatrix}
a_{11} &a_{12} \\[10pt]
a_{21} &a_{22}+b_{12}
\end{pmatrix}, \qquad
{\renewcommand\arraystretch{2}
\begin{pmatrix}
a_{11} &a_{12} \\
a_{21} &a_{22}+b_{12}
\end{pmatrix}
}
\end{equation*}
かな。