# Parenthesis don't appear in beamer

I'd like to show parenthesis in equation environment for beamer presentation. I don't know because it not appear.

\documentclass{beamer}
\usepackage[utf8]{inputenc}
\usepackage[portuguese]{babel}
\usepackage{mathtools}

\usepackage{upgreek}
\usepackage{amsmath}
\usepackage{bbold}
\usepackage[subnum]{cases}
\usepackage{MnSymbol}
\usepackage{lmodern} % required to show the problem

\usepackage{ragged2e}
\usepackage{etoolbox}

\apptocmd{\frame}{}{\justifying}{}
\newcommand{\bs}{\mathbf}

\begin{document}
\section{Introdução}
%\subsection{First Subsection}
\begin{frame}{Unified Particle Swarm Optimizer - UPSO}
\justifying
\setbeamercolor{block title}{fg=white,bg=red!75!black}
PSO tradicional foi proposto por Eberhart, R. C. and Kennedy, J. (1995) e apresenta as seguintes equações:
\begin{equation*}
\begin{aligned}
v_{i+1} = \omega v_i + r_1c_1 (\bs{lbest_i} - \bs{x_i}) + r_2c_2 (\bs{gbest_i} - \bs{x_i})\\
x_{i+1} = x_i + v_{i}\\
\end{aligned}
\end{equation*}

\end{block}
\end{frame}
\end{document}

• In instance, (\bs{lbest_i} - \bs{x_i}) these parentheses ( and ). Mar 28, 2017 at 5:10
• This is a miracle. After running your mwe I really get these parentheses. You may have a look into the log-file: Are there any warnings regarding fonts? Mar 28, 2017 at 5:15
• Yes, I tried more once and they appeared. But in my real problem still don't appear. Mar 28, 2017 at 5:18
• The question is if they appear in the code that you provide here. Mar 28, 2017 at 5:20

When you change the order of the packages lmodern and MnSymbol to
\usepackage{lmodern}