Recently I have been trying to post a matrix and I used what is shown at:

https://math.meta.stackexchange.com/questions/5020/mathjax-basic-tutorial-and-quick-reference

But the outcome is what you can see:

$$

```
\begin{matrix}
1 & x & x^2 \\
1 & y & y^2 \\
1 & z & z^2 \\
\end{matrix}
```

$$

Any solution?

Thank you