%% 
%%  An UIT Edition example
%% 
%%  Example 04-26-1 on page 137.
%% 
%%  Copyright (C) 2012 Vo\ss 
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 

% Show page(s) 1,2,3

%% ==== 
\PassOptionsToClass{}{beamer}
\documentclass{exabeamer}
\usepackage[utf8]{inputenc}

%\StartShownPreambleCommands
\usepackage{amsmath}
%\StopShownPreambleCommands

\begin{document}
\begin{frame}{Equation lines as overlays}
Text before the equation\ldots
\begin{align}
  y &= a \tag{constant}\\
  \uncover<2->{y &= a\cdot x\tag{linear}\\}
  \uncover<3->{y &= a\cdot x+b\cdot x^2\tag{quadratic}\\}
  \notag% empty line necessary for beamer
\end{align}\vspace{-1.5\normalbaselineskip}% remove line feed through notag
Text after the equation\ldots
\end{frame}
\end{document}