%% 
%%  An UIT Edition example
%% 
%%  Example 10-10-7 on page 226.
%% 
%%  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}}
\StartShownPreambleCommands
\usepackage{amsmath}
\newlength{\myVSpace}\setlength{\myVSpace}{1ex}
\newcommand\xstrut{\rule[-0.5\myVSpace]{0pt}{\myVSpace}}
\StopShownPreambleCommands
\begin{document}
\begin{align*}
\left.\begin{aligned}
\xstrut\varphi\left(z_1\right) &= P\frac{-i}{2\left(s_1-s_2\right)\left(1+is_1\right)}
  \left[1-\frac{z_1}{\sqrt{z_1^2-R^2\left(1+s_1^2\right)}}\right]\\
\xstrut\psi\left(z_2\right) &= P\frac{+i}{2\left(s_1-s_2\right)\left(1+is_2\right)}
  \left[1-\frac{z_2}{\sqrt{z_2^2-R^2\left(1+s_2^2\right)}}\right]
\end{aligned}\right\} \text{some text}
\end{align*}

\addtolength{\myVSpace}{3cm}% see preamble for definition
\begin{align*}
\left.\begin{aligned}
\xstrut\varphi\left(z_1\right) &= P\frac{-i}{2\left(s_1-s_2\right)\left(1+is_1\right)}
  \left[1-\frac{z_1}{\sqrt{z_1^2-R^2\left(1+s_1^2\right)}}\right]\\
\xstrut\psi\left(z_2\right) &= P\frac{+i}{2\left(s_1-s_2\right)\left(1+is_2\right)}
  \left[1-\frac{z_2}{\sqrt{z_2^2-R^2\left(1+s_2^2\right)}}\right]
\end{aligned}\right\} \text{some text}
\end{align*}
\end{document}