How can I make the radical end at the same level with 11...1 and 44...4 and put the underbrace below the radical? I have this: \sqrt{ \underbrace{11...1}_n\underbrace{44...4}_{2n}}

• It is not clear what you want. maybe \underbrace{\sqrt{}}? – Sigur Nov 3 '18 at 19:17
• Something like this, but I have two separate underbarce under the same radical, and I need them to remain exactly below that numbers – Cristina Maria Pacurar Nov 3 '18 at 19:26

Insert the \sqrt with \phantom content and then overlap the \underbraced content using \mathllap (from mathtools):

\documentclass{article}

\usepackage{mathtools}

\begin{document}

$\sqrt{\phantom{11 \cdots 1 \, 44 \cdots 4}} \mathllap{\underbrace{11 \cdots 1}_n\underbrace{44 \cdots 4}_{2n}}$

\end{document}


Just for the sake of variety, here's a solution that uses \smash[b]{...} and \vphantom to achieve the typographic objective. The \vphantom directive serves to insert what's called a typographic strut, placed outside the square-root term.

\documentclass{article}
\usepackage{amsmath} % for "\smash[b]{...}" macro
\begin{document}
$\sqrt{\smash[b]{\underbrace{11...1}_n\underbrace{44...4}_{2n}}} \vphantom{\underbrace{1}_{n}}$
\end{document}

• This is how I'd do it, too. – egreg Nov 3 '18 at 21:59