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\begin{bmatrix}
1 & 2 & 3 \\
a & b & c \\
a & b & c \\
\end{bmatrix}
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\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
M=
\begin{bmatrix}
1 & 2 & 3 & 4 & 5 \\
3 & 4 & 5 & 6 & 7
\end{bmatrix}
\]
\end{document}
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% Plain matrix
\begin{matrix}
1 & 2 & 3\\
a & b & c
\end{matrix}
% Parantheses matrix
\begin{pmatrix}
1 & 2 & 3\\
a & b & c
\end{pmatrix}
% Square bracket matrix
\begin{bmatrix}
1 & 2 & 3\\
a & b & c
\end{bmatrix}
% Braces matrix (curly brackets matrix)
\begin{Bmatrix}
1 & 2 & 3\\
a & b & c
\end{Bmatrix}
% Pipes
\begin{vmatrix}
1 & 2 & 3\\
a & b & c
\end{vmatrix}
% Double pipes
\begin{Vmatrix}
1 & 2 & 3\\
a & b & c
\end{Vmatrix}
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\begin{equation*}
A_{m,n} =
\begin{pmatrix}
a_{1,1} & a_{1,2} & \cdots & a_{1,n} \\
a_{2,1} & a_{2,2} & \cdots & a_{2,n} \\
\vdots & \vdots & \ddots & \vdots \\
a_{m,1} & a_{m,2} & \cdots & a_{m,n}
\end{pmatrix}
\end{equation*}
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Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Fonts]
"Segoe UI (TrueType)"=""
"Segoe UI Bold (TrueType)"=""
"Segoe UI Bold Italic (TrueType)"=""
"Segoe UI Italic (TrueType)"=""
"Segoe UI Light (TrueType)"=""
"Segoe UI Semibold (TrueType)"=""
"Segoe UI Symbol (TrueType)"=""
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\FontSubstitutes]
"Segoe UI"="NEW-FONT"