What is wrong with this super simple formula? [closed]

Maybe I am tired and cannot figure out this simple problem. Here is my short MWE

\documentclass [11 pt, xcolor=pdftex,x11names,table]{beamer}

\begin{document}
\begin{frame}
\begin{block}{Approximation for expected waiting time}
$T_q \approx a \times \frac{u^\sqrt{2(c+1)}}{1-u} \times \frac{CV^2_a+CV^2_p}{2}$
\end{block}
\end{frame}

\end{document}


when I try to compile it, I get Missing{inserted \end{frame}

Am I making a mistake?

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closed as too localized by egreg, Claudio Fiandrino, Stefan Kottwitz♦Feb 5 '13 at 9:06

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The superscript needs to be in {...}, so you'll have to use u^{\sqrt{2(c+1)}}. –  Jake Feb 5 '13 at 8:45
Jake is right. I don't think there's a 11 pt option in beamer; on the other hand in all classes that support it, it should be 11pt without a space. –  egreg Feb 5 '13 at 8:49
Since Jake's comment should work fine, and it's just a small mistake, there's no need to keep the question open, so we will close it. –  Stefan Kottwitz Feb 5 '13 at 9:06
Thank you for your help :) –  N Nik Feb 5 '13 at 19:33