I want to use a matrix environment that is included in an outer
environment, so:

```
Environment:
\begin{equation*}
\left|
\begin{matrix}
a_1 & b_1\\
a_2 & b_2
\end{matrix}
\right|
\end{equation*}

Display--math:
\[
\left|
\begin{matrix}
a_1 & b_1\\
a_2 & b_2
\end{matrix}
\right|
\]

Inline--math:
\(
\left|
\begin{matrix}
a_1 & b_1\\
a_2 & b_2
\end{matrix}
\right|
\)
```

But for the second and third cases (display-math and inline-math) the
preview and export to latex are failed:

exported LaTeX:

```
Environment:
\begin{equation*}
\left|
\begin{matrix}
a_1 & b_1\\
a_2 & b_2
\end{matrix}
\right|
\end{equation*}

Display--math:
$\backslash$[
\left|
\begin{matrix}
a_1 & b_1\\
a_2 & b_2
\end{matrix}
\right|
$\backslash$]

Inline--math:
$\backslash$(
\left|
\begin{matrix}
a_1 & b_1\\
a_2 & b_2
\end{matrix}
\right|
$\backslash$)
\end{document}
```

org-mode preview:

[image: preview.png]

Emacs  : GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.14)
 of 2020-03-26, modified by Debian
Package: Org mode version 9.3.8 (9.3.8-1-g13dfab-elpaplus @
/home/sd/.emacs.d/elpa/26.3/develop/org-plus-contrib-20200914/)

It is reproduces with Org mode 9.4 also
https://emacs.stackexchange.com/q/60765/13323