# \begin{align} not working when centering math equation

I've read a few posts here about center math equations and all of them make use of

\begin{align} *Math symbols* \end{align}

Now I've included the \usepackage{amsmath} before the begin document line. But I keep getting this error:

Any ideas guys? I'm a latex noob

Here is some code:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\section{Situation 1}

\begin{align}
$J_{(j)} = \sum\limits_{i:r(i,j)=1} ((\theta\textsuperscript{(j)})\textsuperscript{T}x\textsuperscript{(i)} - Y_{i,j})^2 + \frac{\lambda}{2}\sum\limits_{k=1}^n(\theta_k\textsuperscript{(j)})^2$
\end{align}

\end{document}

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Can you post a MWE (see here) that illustrates your problem? A basic program works for me...: \documentclass{article} \usepackage{amsmath} \begin{document} \begin{align} x = y \end{align} \end{document} – cslstr May 22 '14 at 16:07

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