how can I make equations smaller in TeX?

how can I make equations smaller in TeX? For example, I want to use the equation environment as follows:

\begin{equation}
long equation here
\end{equation}

but then it's displayed in a way that's too large to fit in the margin. I get around this by using:

$ long equation here $

but then I don't get the automatic numbering and all the other nice features of equation environments.

secondly, how can I suppress equation numbering for specific equations in \开发者_开发知识库begin{equation}\end{equation}? I'd like equations with no displayed numbers to not count to the total (so if the first 3 equations' numbers suppressed, but the 4th isn't, the 4th equation should be labeled "1").

thanks.

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If you like the results you're getting from $ eqn $, you can get this by putting \textstyle in your equation environment.

To suppress numbering use "*": \begin{equation*} ... \end{equation*}. You can also use \notag on individual equations in an environment (e.g. align).

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but then it's displayed in a way that's too large to fit in the margin.

You're not trying to write the proof of Fermat's Last Lheorem, are you? :-)

Assuming you meant that the equation overflows to the margins, and also assuming you want to avoid that rather than change the font, I would suggest amsmath. For example, you can write a long equation like this:

\begin{multline}
  A = \lim _{n\rightarrow \infty }\Delta x\left( a^{2}+\left( a^{2}+2a\Delta x
    +\left( \Delta x\right) ^{2}\right)\right.\\
  +\left( a^{2}+2\cdot 2a\Delta x+2^{2}\left( \Delta x\right) ^{2}\right)\\
  +\left( a^{2}+2\cdot 3a\Delta x+3^{2}\left( \Delta x\right) ^{2}\right)\\
  + \ldots\\
  \left.+\left( a^{2}+2\cdot (n-1)a\Delta x +(n-1)^{2}\left( \Delta x\right) ^{2}\right) \right)\\
  = \frac{1}{3}\left( b^{3}-a^{3}\right)
\end{multline}

(Example taken from Mathmode: a must if you want to typeset good math.) There are many other environments in amsmath: align and variations of it for aligning across lines, gather to gather multiple equations together, multline (note, no i) for a multi-line equation, split, etc.

To answer your second other question: you can get a non-numbered equation by using the starred form of the equation environment:

\begin{equation*}
    E = mc^2
\end{equation*}

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Shall I understand it that displaymath environment (called by equation environment) typesets your math too wide but environment math (called by $formulae$ fo example) typesets it right?

If so, there are commands that can switch its argument's displaymath mode to math mode and vice versa.

For inducing math style in displaymath you can use \textstyle{} command. For inducing displaymath style in math you can use \displaystyle{} command.

So for your task:

\begin{equation}\textstyle{
neverending formulae
}\end{equation}

I hope it will do what you want.