# How to add a left-hand brace to this system of equations?

How to

My code

\documentclass[12pt,a4paper]{article}
\usepackage{amsmath}
\begin{document}
\begin{alignat}{3}
a_1x &+ b_1y &&+ c_1z &&= d_1 \label{eq1}\\
a_2x &+ b_2y &&+ c_2z &&= d_2 \label{eq2}\\
a_3x &+ b_3y &&+ c_3z &&= d_3 \label{eq3}
\end{alignat}
From the equation \eqref{eq1} we have
\end{document}

• Look at the documentation of empheq Commented Sep 23, 2023 at 9:11

The following solution employs the empheq package and its eponymous environment.

Note that it's not necessary to employ {alignat}{3} for the equations at hand -- align will do just fine.

\documentclass[12pt,a4paper]{article}
\usepackage{empheq} % 'empheq' loads 'amsmath' automatically

\begin{document}
\begin{empheq}[left=\empheqlbrace]{align}
a_1x + b_1y + c_1z &= d_1 \label{eq1} \\
a_2x + b_2y + c_2z &= d_2 \label{eq2} \\
a_3x + b_3y + c_3z &= d_3 \label{eq3}
\end{empheq}
From equation \eqref{eq1} we have \dots
\end{document}


With {DispWithArrows} of witharrows.

\documentclass[12pt,a4paper]{article}
\usepackage{witharrows}
\usepackage{amsmath}

\begin{document}
\begin{DispWithArrows}<>
a_1x + b_1y + c_1z &= d_1 \label{eq1} \\
a_2x + b_2y + c_2z &= d_2 \label{eq2} \\
a_3x + b_3y + c_3z &= d_3 \label{eq3}
\end{DispWithArrows}
From equation \eqref{eq1} we have \dots
\end{document}