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answered 5 years ago
On a code cell, show(LatexExpr("\sqrt{2}")) just works. Perhaps did you forget the closing quotes.
show(LatexExpr("\sqrt{2}"))
Note that you can add longer text by changing the type of a cell to "markdown" (instead of "code"), there, you can just add latex code as $\sqrt{2}$.
$\sqrt{2}$