I'm aware that you can label a single line with \tag:


But can you do this with simultaneous equations? For example, each of the following in:

$$\begin{cases} 2x+3y=5 \\ x-y=19 \end{cases}$$


2 Answers 2


One option for you: You can use the "align" environment. The symbol, in the first case, that I'll align is =. To do that, for every occurrence of $=$, precede it with & separate lines with \\ or \\ \\ as desired, but at the end of each line to be, prior to \\, you can use \tag{*} to label each and every line.

For example, given the following code:

\begin{align} 2x+3y &= 5 \tag{1} \\ x-y &=19\tag{2} \end{align}

We get $$\begin{align} 2x+3y &= 5 \tag{1} \\ x-y&=19\tag{2} \end{align} $$

In order to left align the equations, we move the & to the beginning of each equation, as follows:

\begin{align} & 2x+3y = 5 \tag{1} \\ & x-y =19\tag{2} \end{align}

\begin{align} & 2x+3y = 5 \tag{1} \\ & x-y =19\tag{2} \end{align}

There are so many neat things you can do with formatting. I've learned many of those neat things on this site. Look around at other posts; e.g., search systems of equations, and look at the answers; when you see something you'd like to replicate, hover over it, right-click, click "Show Math As: and then click "Tex Commands"

  • $\begingroup$ Thank you for taking the time and answering. I would still like to have the left bracket symbolic of simultaneous equations however... is there a way to do that? $\endgroup$ Commented Aug 21, 2017 at 22:08
  • 2
    $\begingroup$ Try this: \begin{cases} 2x+3y=5 & (1) \\ x-y=19 & (2)\end{cases} to get \begin{cases} 2x+3y=5 & (1) \\ x-y=19 & (2)\end{cases} $\endgroup$
    – amWhy
    Commented Aug 21, 2017 at 22:14
  • $\begingroup$ That's an improvisation. You can use & to describe or label the the equation. $\endgroup$
    – amWhy
    Commented Aug 21, 2017 at 22:15
  • $\begingroup$ Yep that's the only solution I've come up with myself. It gets a little hazy if the two equations don't have exactly the same line length, but it is what it is.... $\endgroup$ Commented Aug 21, 2017 at 22:16
  • $\begingroup$ Note, though, that using & (1) and &(2) the labels align. You can get more space by ending each equation with & & (1), etc. $\endgroup$
    – amWhy
    Commented Aug 21, 2017 at 22:20
  • $\begingroup$ Indeed that seems to be the best solution. Nothing so nice as using the tag though. $\endgroup$ Commented Aug 21, 2017 at 22:22
  • $\begingroup$ :O Never knew you could use multiple ampersands like that. $\endgroup$ Commented Aug 21, 2017 at 23:42

$$ \begin{align} A + B & = C \\ D + E & = F \\ G + H & = I \\ J + K & = L \end{align} \tag 1 $$

Here is the code for what appears above.

A + B & = C \\
D + E & = F \\
G + H & = I \\
J + K & = L
\end{align} \tag 1

If you put \tag 1 before rather than after \begin{align} then the number is on the right after the first line.

$$\begin{cases} 2x+3y=5 \\ x-y=19 \end{cases} \tag 1 $$

  • $\begingroup$ I think the asker is looking for a way to number each equation in the set of simultaneous equations. So given your example, we have both equations identified as (1) ? $\endgroup$
    – amWhy
    Commented Aug 23, 2017 at 16:37
  • $\begingroup$ @amWhy : The poster does use the word "each" and I was aware that that was probably the immediate concern. But $(1)$ several people had already dealt with that and $(2)$ that's not substantially different from what is done with just one line: you merely put a tag on each line separately, and $(3)$ it is sometimes worth knowing about what I point out in my posting. $\endgroup$ Commented Aug 23, 2017 at 20:08
  • $\begingroup$ I agree that what you say is worth knowing. Please understand, I did not down-vote your answer. $\endgroup$
    – amWhy
    Commented Aug 23, 2017 at 20:11

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