LaTeX Document Using A5 Page size

\documentclass[12pt]{article}
\usepackage[a5paper]{geometry}
\begin{document}
\begin{equation}
(\alpha + \beta)2 = \alpha 2 + \beta 2 + 2\alpha\beta
\end{equation}
\[
\int\limits_0^{2\pi } {\phi dt} 
\]
\begin{tabular}{|l|l|l|l|}
\hline
Heading1 & Heading2 & Heading3 & Heading4 \\ 
\hline
1 & 2 & 3 & 4 \\ 
\hline
5 & 6 & 7 & 8 \\ 
\hline
9 & 10 & 11 & 12 \\ 
\hline
\end{tabular}
$$\frac{1}{{x}^{3}\,{\left( b\,x+a\right) }^{\frac{1}{3}}}$$
 
 
\end{document}