%% %% An UIT Edition example %% %% Example 10-09-10 on page 220. %% %% Copyright (C) 2010 Herbert Voss %% %% 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 %% \documentclass[]{exaarticle} \pagestyle{empty} \setlength\textwidth{375.57637pt} \AtBeginDocument{\setlength\parindent{0pt}} \setcounter{equation}{31} \renewcommand\theequation{10.\arabic{equation}} \StartShownPreambleCommands \usepackage{amsmath} \StopShownPreambleCommands \begin{document} \begin{align} \sum_{i=1}^\infty \frac{1}{i} &= 1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4} +\frac{1}{5}+\frac{1}{6}+\frac{1}{7}+\frac{1}{8}+\frac{1}{9} +\cdots+\frac{1}{16}+\cdots\\ & \ge 1+\frac{1}{2}+\underbrace{\frac{1}{4}+\frac{1}{4}}_{\frac{1}{2}} +\underbrace{\frac{1}{8}+\frac{1}{8}+\frac{1}{8}+\frac{1}{8}}_{\frac{1}{2}} +\underbrace{\frac{1}{16}+\cdots+\frac{1}{16}}_{\frac{1}{2}}+\cdots\\ &= 1+\frac{1}{2}+\frac{1}{2}+\frac{1}{2}+\frac{1}{2}+\cdots\to\infty \quad\rule{1ex}{1ex} \end{align} \end{document}