\documentclass[]{standalone}
\usepackage{adjustbox}
\usepackage{amsmath}
\usepackage{graphicx}
\begin{document}
$
\left[
\begin{array}{c|c}
I   &  \\
\vdots & \mbox{RREF}' \\
I   &
\end{array}
\right],\quad
\left[
\begin{array}{c|c}
I      &              \\
\vdots & \mbox{RREF}' \\
I      & \\ \hline
\sigma &  * \ldots *  
\end{array}
\right]
\mbox{ and }
\left[
\begin{array}{c|c}
I      &               \\
\vdots &  \mbox{RREF}' \\
I      & \\ \hline
\sigma_1 &  * \ldots * \\
\sigma_2 &  * \ldots * \\
\end{array}
\right]
$ 
\end{document}