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% this is the default PlanetMath preamble. as your knowledge
% of TeX increases, you will probably want to edit this, but
% it should be fine as is for beginners.
% almost certainly you want these
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{amsfonts}
% used for TeXing text within eps files
%\usepackage{psfrag}
% need this for including graphics (\includegraphics)
%\usepackage{graphicx}
% for neatly defining theorems and propositions
%\usepackage{amsthm}
% making logically defined graphics
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% there are many more packages, add them here as you need them
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\begin{document}
Let $a$ be a number not equal to zero. Then for all $n \in \mathbb{N}$, we have that $a^n$ is the product of $a$ with itself $n$ \PMlinkescapetext{times}. Using the fact that the integer 1 is a multiplicative identity, ($a\cdot 1=a$ for any $a$), we can write
\begin{displaymath}
a^n \cdot 1=a^n=a^{n+0}=a^n\cdot a^0,
\end{displaymath}
where we have used the properties of exponents under multiplication. Now, after canceling a factor of $a^n$ from both sides of the above equation, we derive that $a^0=1$ for any non-zero number.