When , there are two solutions to and they are

You need set `mathjax: true`

in the *_config.yml* or the markdown’s front matter to **enable** it.

**After MathJax enabled**, you can set `mathjax_autoNumber: true`

to have equations be numbered automatically, You can use `\notag`

or `\nonumber`

to prevent individual equations from being numbered.

**markdown:**

```
When $$a \ne 0$$, there are two solutions to $$ax^2 + bx + c = 0$$ and they are
$$x_1 = {-b + \sqrt{b^2-4ac} \over 2a}$$
$$x_2 = {-b - \sqrt{b^2-4ac} \over 2a} \notag$$
```

**front matter:**

```
---
...
mathjax: true
mathjax_autoNumber: true
---
```

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