# how to use onslide to apply underbrace beneath operation

I am trying to apply a simple transition in beamer, after writing the operation without having to repeat the equation every time. I try the code :

\begin{frame}

\frametitle{Exemples}
\begin{exampleblock}{2.1.2.Exemples}
Effectuer les opérations suivantes:
\begin{multicols}{2} % two columns
\begin{itemize}[<+->]

\item<1-> $A = \underbrace{(15 - 7)\onslide<2>}- 6 + 3$
\item<2-> $A = \underbrace{8 - 6\onslide<3>} + 3$
\item<3-> $A = \underbrace{2 + 3\onslide<4>}$
\item<4-> $A = 5$

\columnbreak

\item<5-> $B =\underbrace{(9 + 13)\onslide<2->}- 7.2 - 1$
\item<6-> $B = \underbrace{22 - 7.2} - 1$
\item<7-> $B = \underbrace{14.8 - 1}$
\item<8-> $B = 13.8$

\end{itemize}
\end{multicols}
\end{exampleblock}
\end{frame}


I am trying to make the equations A and B appear at first, let the students have a time of reflection, then show the correction step by step, first by showing the underbrace beneath each operation, then transition to display the next line $A = 8 - 6 + 3$ ... so I use \only<1-> but its not working, I think its a basic question, Now I already inserted the transition between item correctly and I get the result:

I am just not familiar with this \onslide<2> action yet, please help fix this problem ,

thanks for the help !

Here is a (somewhat lengthy) option that sequentially displays the elements with the appropriate \underbrace constructions frame-by-frame:

\documentclass{beamer}

\usetheme{Warsaw}
\usepackage{multicol,mathtools,eqparbox}

% https://tex.stackexchange.com/a/34412/5764
\makeatletter
\NewDocumentCommand{\eqmathbox}{o O{c} m}{%
\IfValueTF{#1}
{\def\eqmathbox@##1##2{\eqmakebox[#1][#2]{$##1##2$}}}
{\def\eqmathbox@##1##2{\eqmakebox{$##1##2$}}}
\mathpalette\eqmathbox@{#3}
}
\makeatother

\begin{document}

\begin{frame}

\frametitle{Exemples}

\begin{exampleblock}{2.1.2.Exemples}
Effectuer les opérations suivantes:
\begin{multicols}{2} % two columns
\begin{itemize}[<+->]

\item $A = \alt<2-> {\eqmathbox[A1]{\underbrace{(15 - 7)}}}% Slide 2+ {\eqmathbox[A1]{\vphantom{\underbrace{(15 - 7)}}(15 - 7)}}% Slide 2 only - 6 + 3$
\item $A = \alt<3-> {\eqmathbox[A2]{\underbrace{\eqmathbox[A1]{8} - 6}}}% Slide 3+ {\eqmathbox[A2]{\vphantom{\underbrace{\eqmathbox[A1]{8} - 6}}\eqmathbox[A1]{8} - 6}}% Slide 3 only + 3$
\item $A = \alt<4-> {\eqmathbox[A3]{\underbrace{\eqmathbox[A2]{2} + 3}}}% Slide 4+ {\eqmathbox[A3]{\vphantom{\underbrace{\eqmathbox[A2]{2} + 3}}\eqmathbox[A2]{2} + 3}}% Slide 4 only$
\item $A = \eqmathbox[A3]{5}$

\columnbreak

\item $B = \alt<6-> {\eqmathbox[B1]{\underbrace{(9 + 13)}}}% Slide 6+ {\eqmathbox[B1]{\vphantom{\underbrace{(9 + 13)}}(9 + 13)}}% Slide 6 only - 7.2 - 1$
\item $B = \alt<7-> {\eqmathbox[B2]{\underbrace{\eqmathbox[B1]{22} - 7.2}}}% Slide 7+ {\eqmathbox[B2]{\vphantom{\underbrace{\eqmathbox[B1]{22} - 7.2}}\eqmathbox[B1]{22} - 7.2}}% Slide 7 only - 1$
\item $B = \alt<8-> {\eqmathbox[B3]{\underbrace{\eqmathbox[B2]{14.8} - 1}}}% Slide 8+ {\eqmathbox[B3]{\vphantom{\underbrace{\eqmathbox[B2]{14.8} - 1}}\eqmathbox[B2]{14.8} - 1}}% Slide 8 only$
\item $B = \eqmathbox[B3]{13.8}$

\end{itemize}
\end{multicols}
\end{exampleblock}
\end{frame}

\end{document}


I'm using boxes captured through eqparbox for measuring equally-sized areas, any change in the maximum width of <stuff> by <tag> in \eqmathbox[<tag>][<align>]{<stuff>} will require a re-compilation.

• THANKS A LOT MAN, I wasted all day trying to find a fix with \onslide but it seems \alt is the way to go Aug 2 at 22:10
• @user2161721: \alt<os>{<default>}{<other>} prints <default> on <os> and <other> otherwise. Aug 3 at 3:28
• indeed, bc I really didn't grasp the principle behind eqparbox, I am having trouble recompiling this one 25+3.5 \times 4 using the same structure, can you endolge me on this one too please Aug 3 at 12:01

\documentclass{beamer}
\setbeamercovered{transparent}
\begin{document}
\begin{frame}
\begin{displaymath}
\onslide<2-> \underbrace{ \onslide<1->
foo
\onslide<2-> }_{bar} \onslide<1->
\text{some more stuff for slide 1}
\end{displaymath}
\end{frame}
\end{document}


its the smartest way to encircle the display the under brace separately