Aligning equations with align*

Question

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?

Answer 1

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

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}