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I wanted to align a set of equations to left. I found on the Internet that you can do it easily with align* environment.

I found it here: http://en.wikibooks.org/wiki/LaTeX/Advanced_Mathematics

So I did it:

\begin{align*}

f(b)-f(a)=&f((b_1,b_2,\dots,b_k))-f((a_1,a_2,\dots,a_k))=\
&=\sum_{i=1}^{k}[f((a_1,\dots,a_{i-1},b_i,\dots, b_k))-f((a_1,\dots,a_i,b_{i+1},\dots, b_k)) 
\end{align*}

Unfortunately, I got bunch of red errors saying that there are missing $s. Why? Doesn't that align* environment provide a math environment already?

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That should not be a problem. Are you including the amsmath package? Regardless, you should never leave an empty line inside align. Also, use &= instead of =& in the first line, and drop the ending =. –  Werner Oct 3 '12 at 22:33

1 Answer 1

You can't have blank lines within an align environment:

enter image description here

Notes:

  • AS Werner (and egreg) commented, you should use &= as opposed to =&.
  • And to answer your other question, you and correct in that you do not use $ within an align as that is already math mode.
  • I removed the 2nd equal sign in the first line as it is not necessary.
  • I added \Big[ and \Big] to provide larger square brackets -- your right bracket was missing.

Code:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align*}
f(b)-f(a) &=f((b_1,b_2,\dots,b_k))-f((a_1,a_2,\dots,a_k))\\
          &=\sum_{i=1}^{k}\Big[f((a_1,\dots,a_{i-1},b_i,\dots, b_k))-f((a_1,\dots,a_i,b_{i+1},\dots, b_k)) \Big]
\end{align*}

\end{document}
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