alignment and numbering of math formulas

I have 3 formulas which should be aligned at the = sign and numbered (1) to (3).

Seems a simple task but trying both \being{equation} with \begin{split} and \being{align} did not work out. I alwasy struggled with the numbering or wit the alignment. Never got it right.

For example my simple equations good look like:

a = x  + y     (1)

b = z - k      (2)

c = j x (z-k)  (3)
= j x b

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Here is specialised numbering and spacing as requested in the comments:

\documentclass{amsart}

\begin{document}
\begin{align}
a &= x + y \tag{1}\\[2ex]
b &= z - k \tag{2}\\[2ex]
c &= j x (z-k) \tag{3}\\
&= j x b \notag
\end{align}
\end{document}


You can change the value 2ex to increase or decrease the spacing.

To get equation numbers on the right instead of the left, use the reqno option to the documentclass amsart (or to the package amsmath if you are not using an ams class).

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Yes, that is how I want it! thanks a lot. I also edited my original post to show you how it should really look like. – Josh Dec 18 '12 at 13:47
\begin{align}
a &= x  + y \\
b &= z - k \\
c &= j x (z-k) \\
&= j x b \notag
\end{align}


That's how I've always done it and it works for me.

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well, but then = j + b gets it's own number which i think is wrong. also as this is part of my 7th chapter is numbers it as (7.1) to (7.4) but I want just (1) to (4). Also is it possible to add a empty line between each formula without adding another numbering tag. Because if I change \\ to \\\\ it numbers the empty line as well – Josh Dec 18 '12 at 13:43
Yeah spotted the last \\ as well – Josh Dec 18 '12 at 13:43
You also need a \notag on the last line to remove the number. – Andrew Swann Dec 18 '12 at 13:43
Updated my answer to show your suggestions. – jlconlin Dec 18 '12 at 13:45