I use markdown editor and mathjax to write math formula, sometimes it cannot show corrected form, here is the example:

$$(A_2)\int_{-\infty}^{+\infty} dx $$

Is this a markdown editor's bug?

When I use Basic Editor,it is OK.

Furthermore, in the Preview of markdown editor, the formula shows OK, but when I finish the editor, the answer shows problem.

Help me, please.