If you have TeX working the syntax is for example
$$ \$\$ $$ \frac{7}{4} $$ \$\$ $$ to produce $$\frac{7}{4}$$
but you can not use TeX everywhere.
With asciimathml the syntax is simple: `7/4` - but it is not used in moodle.org
If you have no tools for maths you can still use html (and css - but it may be difficult, different themes and fonts may cause surprises sometimes) - for example
<ul style="align:center;valign:middle;margin: 0pt; padding: 0pt; list-style-type: none;">
<li>7</li>
<li>─</li>
<li>4</li>
</ul>
to produce
- 7
- ─
- 4
or for example images like