# some text below fraction

I am trying to place some text below the fraction but I am getting the following error:

! Missing $inserted.$ l.5 ...ac{1}{\alpha_{ideal}}}{\text{\leq r{i-1}} }$Code: \documentclass{article} \usepackage{amsmath} \begin{document}$\underbrace{\frac{1}{\alpha_{ideal}}}_{\text{\leq r_{i-1}}}\$
\end{document}


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Remove \text: what under the brace is not text. And add one for ideal: I suppose you don't mean the product of the 5 variables i, d, e, a, l.
\documentclass{article}
$\underbrace{\frac{1}{\alpha_\text{ideal}}}_{\leq r_{i-1}}$