If you are writing a LaTeX snippet you may need to write aligned multiple line equations. New lines (\\) do not work in equation environments. To achieve alignment of equations, use the aligned package.
For example, writing:
\begin{center}
\begin{aligned}
$F$ ={} & $\{F_{x} \in F_{c} : (|S| > |C|)$ \\
& $\cap (\mathrm{minPixels} < |S| < \mathrm{maxPixels})$ \\
& $\cap (|S_{\mathrm{conected}}| > |S| - \epsilon) $\}
\end{aligned}
\end{center}
will produce:


Note: the above multiline equation has math mode defined per line, not globally at the equation level. To do a single equation instead, you can try:
\begin{center}
\[
\begin{aligned}
F ={} & \{F_{x} \in F_{c} : (|S| > |C|) \\
& \cap (\mathrm{minPixels} < |S| < \mathrm{maxPixels}) \\
& \cap (|S_{\mathrm{conected}}| > |S| - \epsilon) \}
\end{aligned}
\]
\end{center}

Further reading
More LaTeX equation examples (fork it!)
LaTeX cheatsheet
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