title: combination/matrix in latex
body: <p>I am trying the write something below in latex and what I am trying seems not working well.</p>
  <pre><code>\documentclass[10pt,english,8pt]{beamer}
  \usepackage{amsmath}
  \begin{document}
  
  \begin{frame}
  
  \begin{itemize}
      \item Observation equation: 
      
   $\begin{pmatrix}
      PD_{s,t}\\ 
      RR_{s,t} 
  \end{pmatrix} = \binom(\gamma_{1}\gamma_{2}) = bla
      
      
  \end{itemize}
  
  \end{frame}
  \end{document}
  </code></pre>
  <p><a href="https://i.stack.imgur.com/DH1FX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DH1FX.png" alt="enter image description here" /></a></p>