How to write underbrace symbol in LaTeX?

Underbrace is a single curly bracket placed below an expression. For example:

LaTeX offers multiple methods to represent this symbol, each with structural differences. This tutorial covers all approaches to help you find answers to your questions.

The \underbrace command in LaTeX works without additional packages, allowing direct use to represent this symbol. For example:

\[ \underbrace{a_1+a_2+a_3+ \cdots + a_n} \]

\[ \underbrace{a_1+a_2+a_3+ \cdots + a_n} \]

Use multiple methods for placing a brace below

Here, multiple packages have been used to demonstrate different methods. Each package contains the same command but differs in structure, as shown in the table below.

Package	Command
MnSymbol	\underbrace{abcd}
fdsymbol	\underbrace{abcd}
stix	\underbrace{abcd}
mathabx	\underbrace{abcd}

Multiple lines expression

You may have noticed that different text, number is written under the underbrace. And to represent this syntax, you need to use a subscript with this command.

\documentclass{article}
\usepackage{stix}
\begin{document}
  \[ \underbrace{a_1+a_2+\cdots+a_n}_{\textit{n term}}+\underbrace{x_1+x_2+\cdots+x_m}_{\textit{m term}} \]
  \[ \underbrace{a^2+2ab+b^2}_{(a+b)^2}=\underbrace{a^2+2a+1}_{(a+1)^2} \]
\end{document}

Output :

And the expression is passed as an argument in the subscript to display it below the curved brace symbol.

To place a curly bracket below a matrix

To place a curly bracket below a matrix, the entire environment must be enclosed within the corresponding command as an argument.

\documentclass{article}
\usepackage{stix,amsmath}
\begin{document}
 \[\underbrace{
   \begin{pmatrix}
    a_{1,1} & a_{1,2} & \cdots & a_{1,n} \\
    a_{2,1} & a_{2,2} & \cdots & a_{2,n} \\
    \vdots  & \vdots  & \ddots & \vdots  \\
    a_{m,1} & a_{m,2} & \cdots & a_{m,n} 
   \end{pmatrix}}_{m \times n}\]
\end{document}

Output :

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