Error when typing Matrix and Binomial coefficients

Question

New guy here, I am just trying to study LaTeX from the very beginning. I am using TexShop on a Mac, and now I am reading George Grätzer's Short Course.

Here's my question, when I type Binomial coefficients or Matrices in TexShop, I get an error. What's my problem?

This is my code

\documentclass[11pt, oneside]{article}      
\usepackage{geometry}                       
\geometry{letterpaper}                          
%\geometry{landscape}                       
%\usepackage[parfill]{parskip}           
\usepackage{graphicx}               
                            %convert eps --> pdf in  pdflatex       
\usepackage{amssymb}

\title{Brief Article}
\author{The Author}
%\date{}                            

\begin{document}
\maketitle
%\section{}
%\subsection{}


\[
   \binom{ \frac{n^{2} - 1}{2} }{n + 1}
\]

 \[
                 \begin{matrix}
                   a + b + c & uv    & x - y & 27\\
                   a + b     & u + v & z     & 134
                 \end{matrix}
\]


\end{document}  

Answer 1

Add the line \usepackage{amsmath} in the preamble. amssymb is meant for special symbols.

\documentclass[11pt, oneside]{article}      
\usepackage{geometry}                       
\geometry{letterpaper}                          
%\geometry{landscape}                       
%\usepackage[parfill]{parskip}           
\usepackage{graphicx}               
%                            convert eps --> pdf in  pdflatex        
\usepackage{amsmath}         % Add this line!!!!!
\usepackage{amssymb}

\title{Brief Article}
\author{The Author}
%\date{}                            

\begin{document}
\maketitle
%\section{}
%\subsection{}

\[
   \binom{ \frac{n^{2} - 1}{2} }{n + 1}
\]

 \[
                 \begin{matrix}
                   a + b + c & uv    & x - y & 27\\
                   a + b     & u + v & z     & 134
                 \end{matrix}
\]

\end{document}