The universal solution is using the HTML tag <sup>
, as suggested in the main answer.
However, the idea behind Markdown is precisely to avoid the use of such tags:
The document should look nice as plain text, not only when rendered.
Another answer proposes using Unicode characters, which makes the document look nice as a plain text document but could reduce compatibility.
Finally, I would like to remember the simplest solution for some documents: the character ^
.
Some Markdown implementation (e.g. MacDown in macOS) interprets the caret as an instruction for superscript.
Ex.
Sin^2 + Cos^2 = 1
Clearly, Stack Overflow does not interpret the caret as a superscript instruction. However, the text is comprehensible, and this is what really matters when using Markdown.