Mathjax can't scale left bracket without having a right one

[Maxkand]

Things I have tried

i have tried a lot of things. The best solution i have found is to use

$$\begin{cases}
a
b \\
c \\
d
\end{cases}$$

But this is not what i want because i want the lines to be aligned
I know this is possible by using \left\{ and \right\} but the thing is i only want one at the left. Writing

$$\left\{ \begin{eqnarray} 
x_1 + 2x_2 + 3x_3 = 4 \\
5x_2 + 6x_3 = 7 \\
8x_3 = 9
\end{eqnarray}

doesn’t work

What I’m trying to do

I want to create a left curly bracket that scales over 4 lines or more without a right one to write equation systems.
Basically i want this

$$\Bigg\{ \begin{eqnarray} 
x_1 + 2x_2 + 3x_3 = 4 \\
5x_2 + 6x_3 = 7 \\
8x_3 = 9
\end{eqnarray}$$

but with a left bracket that scales (or a way to make it even bigger but “Bigg” is the maximum apparently)

[saf-dmitry]

This is a normal LaTeX behavior. In order to know how to scale the left delimiter, LaTeX (and MathJax) must know, where the content of the enclosed block ends. In LaTeX there are so called “invisible” delimiters \right. and \left., that are used to match a corresponding opening/ closing delimiter. You can use them when you need a delimiter only on one side of the expression:

$$
\left\{
\begin{eqnarray}
  x_1 + 2x_2 + 3x_3 & = 4 \\
        5x_2 + 6x_3 & = 7 \\
               8x_3 & = 9
\end{eqnarray}
\right.
$$

[Maxkand]

Thank you so much ! I feel stupid now, i should have experimented more sorry.
I didn’t read anywhere that you could use a dot to signifie you don’t want anything at one end…

[saf-dmitry]

I didn’t read anywhere that you could use a dot to signifie you don’t want anything at one end…

For example, the book The Not So Short Introduction to LaTeX (highly recommended for all LaTeX noobs) mentions “dot delimiters” on p. 89.