Just surround your code with [tex] and [/tex]. The board sets math mode automatically, so don't use dollar signs around everything.

For example:

ProducesCode:[tex]\sum_{n=1}^\infty\frac1n=\frac{\pi^2}6[/tex]

Use \text{} to get regular non-math text. There are limits on the number of characters and the size of each image, so you may need to break things up into several sections. For full paragraphs of text, like in your PDF, post the non-math text outside of the [tex] tags.