# Centering a group of equations and the usepackage, environments etc?

I am running into trouble for nicely centering a group of equations in a Mathematics paper written in LaTeX. Say, I want to get the following group of equations 1) written one below another, 2) in the middle of the page to make things look better, 3) with the equality signs one right below the other. For example , say I want to type x^2 - 4 = 0, ( x+2) ( x-2) = 0, x = 2, -2 satisfying the properties 1),2), 3).

a) What packages, and document class should I use ?

b) I need to define any environment before \begin{document}?

c) What are the exact commands that would do the job nicely ?

d) Should I use  or just  ? e) Also, for the above, can I nicely insert the implication symbol => ? I tried \\[...]\\, it didn't work for some reason, also tried to include amsmath as a package, and then tried \\begin{align*}....\\end{align*}, didn't work. Also I think I tried ... and that centered the equation, but not keeping the equality symbols one right below the other, and also changed the output for the equations to a smaller font compared to the rest of the paper.

What exactly should I use that would do the job nicely ? Thanks a lot in advance !

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a) The amsmath package offers you a wide range of environments and commands to typeset equations; read its documentation and also the mathmode document.

b) No.

c) See code below.

e) Where exactly do you want to insert the symbol?

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align*}
x^2 - 4 &= 0 \\
( x + 2) ( x - 2 ) &= 0 \\
x &\in \{ 2, -2 \}.
\end{align*}

\end{document}


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Gonzalo, first off, thanks ! One quick question : should I use $sign in every line before a paragraph ends and begins, or should I just use$ sign in the beginning of the equation, keep inserting \\\ symbols to go to a different paragraphs, and then use $sign right at then end again ? Thanks again ! – Mathmath May 15 '12 at 2:04 @Mathmath: the $ symbol is reserved and it is used to enter/exit in-line math mode. So you should use $...$ to write in-line (i.e., not displayed) math: for example: a function is even if $f(-x)=f(x)$, for all $x$ (although the proper LaTeX way would be a function is even if $$f(-x)=f(x)$$, for all $$x$$). Never use \\ to increase space between paragraphs (See tex.stackexchange.com/q/51722/3954). To end a paragraph, leave a blank line in the code. –  Gonzalo Medina May 15 '12 at 2:20