Properly typeset a system of equations

Question

I'm trying to typeset a system of linear equations which has multiple place to be aligned. Below is what I have achieved so far:

\documentclass{article}
\usepackage{mathtools}
\begin{document}
[
    \left{
        \begin{alignedat}{5}
            &x &+& &&y &=& &&0\
            2&x &+& 3&&y &=& &&0
        \end{alignedat}
    \right.
]
\end{document}

As you can see from the above picture, the spacing seems to be a little bit strange (though I cannot tell exactly where is wrong). Is there some way to improve this result? (I'm using alignat in the MWE, but you may also use array or other methods if better result can be gained.)

I think this has been asked many times, no? One quick way in LaTeX is to use the systeme package. — mickep, Sep 17 '22 at 16:32
@mickep Thank you for the recommendation, this seems to be a pretty nice package. — Jinwen, Sep 17 '22 at 16:35

score 5 · Answer 1 · answered Sep 17 '22 at 21:21

5

Here's a systeme-based solution.

\documentclass{article}
\usepackage{systeme}
\begin{document}
\[
\systeme{x+y=0,2x+3y=0}
\]
\end{document}

answered Sep 17 '22 at 21:21

Mico

506,678

Zarko · Answer 2 · 2022-09-17T18:08:56.497

3

Two examples:

use of array
use of a bit simplified your code:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
[\setlength\arraycolsep{1pt}
    \left{
        \begin{array}{rcrl}
            x & + &  y & = 0\
           2x & + & 3y & = 0
        \end{array}
    \right.
]
or
[
    \left{
        \begin{alignedat}{3}
            x & + {} &  y & = 0\
           2x & + {} & 3y & = 0
        \end{alignedat}
    \right.
]
\end{document}

Edit: Considered is @David Carlisle comment.

edited Sep 17 '22 at 18:08

answered Sep 17 '22 at 17:13

Zarko

296,517

Thank you for this. Would you mind explaining a little regarding how does your alignedat work? I used to think that each line of the content of alignedat start with a single &, and then has two &s each time. – Jinwen Sep 17 '22 at 17:37
@DavidCarlisle, you are right. Corrected now. – Zarko Sep 17 '22 at 18:09
@Jinwen, good explanation about alinedat you can find in https://tex.stackexchange.com/questions/96124/what-is-the-mandatory-argument-of-alignedat-for – Zarko Sep 17 '22 at 18:28

score 3 · Accepted Answer · answered Sep 17 '22 at 18:15

I would probably use this form, with alignment points between the coefficients and the variables.

\documentclass{article}
\usepackage{mathtools}
\begin{document}
[
    \left{
        \begin{alignedat}{3}
             &x +{}&  &y &&=0\
            2&x +{}& 3&y &&=0
        \end{alignedat}
    \right.
]
\end{document}

Properly typeset a system of equations

3 Answers3