%% 
%%  Example 07-05-3 
%%  Copyright (C) 2017 Herbert Voss
%% 
%% ==== 
% Show page(s) 1
%% 
%% 
\documentclass[]{screxa}
\pagestyle{empty}
\setlength\textwidth{328.62788pt}
\setlength\parindent{0pt}
\usepackage[T1]{fontenc}
%StartShownPreambleCommands
\usepackage{amsmath,xcolor}
%StopShownPreambleCommands
\begin{document}
\begin{align}
y &= 2x^2 -3x +5\nonumber\\
  & \hphantom{= \ 2\left(x^2-\frac{3}{2}\,x\right. }%
         \textcolor{blue}{%
              \overbrace{\hphantom{+\left(\frac{3}{4}\right)^2- %
                  \left(\frac{3}{4}\right)^2}}^{=0}}\nonumber\\[-11pt]
  &= 2\left(\textcolor{red}{%
        \underbrace{x^2-\frac{3}{2}\,x + \left(\frac{3}{4}\right)^2}}
     \underbrace{-\left(\frac{3}{4}\right)^2 + \frac{5}{2}}\right)\\
  &= 2\left(\qquad\textcolor{red}{\left(x-\frac{3}{4}\right)^2}
     \qquad + \ \frac{31}{16}\qquad\right)\nonumber\\
y\textcolor{blue}{-\frac{31}{8}}
  &= 2\left(x\textcolor{cyan}{-\frac{3}{4}}\right)^2\nonumber
\end{align}
\end{document}
