# Big Parenthesis in an Equation

I have an equation contained inside $...$, which automatically makes a \sum with sub- and superscripts turn big--so that the summation sign looks awkward inside parenthesis. Any idea how to make the parenthesis completely enclose the whole summation?

\documentclass{article}
\begin{document}
We have:
$\sum_{i=1}^n i = (\sum_{i=1}^{n-1} i) + n = \frac{(n-1)(n)}{2} + n = \frac{n(n+1)}{2}$
\end{document}

• Use \left( for the opening bracket and \right) for the closing one. These will automatically adjust their height to fit the contents. Dec 20, 2011 at 6:16
• Related Question: About big parenthesis larger than Bigg. Feb 23, 2013 at 5:27

The usual thing to do is replace ( with \left( and ) with \right), which automatically expand to fit the material between them. Note that every \left... requires a \right... (but the type of bracket may be different, i.e. \left(...\right] also works).

I would typeset your equation as

\begin{equation*}
\sum_{i=1}^n i = \left(\sum_{i=1}^{n-1} i\right) + n =
\frac{(n-1)(n)}{2} + n = \frac{n(n+1)}{2}
\end{equation*} For manual control of sizes (most of the time you won't need these)

( \big( \Big( \bigg( \Bigg(


produce • The environment I use is from the amsmath package, so yours is actually more general. I just find [...] to look messy. Alternatively there is the displaymath environment. Dec 20, 2011 at 6:56
• @jamaicanworm: amsmath defines $...$ to be exactly the same as \begin{equation*}...\end{equation*}. See, literally, the last couple of lines of amsmath.sty.
– Werner
Dec 20, 2011 at 7:26
• @jamaicanworm The shape of the brackets is down to the font I'm afraid. If you don't like the larger curved brackets, try the square ones \left[...\right]. These often look better for larger equations. Another thing to take into account is that you're enclosing something relatively thin in those brackets. I suspect it will only look more natural when there's more between them (try putting the n to the left of the sum and loosing the brackets altogether). Dec 20, 2011 at 7:29
• I would be a bit careful using \left/right around sums etc. because they often become too large. I tend to recommend users to: Scale the fences (parenteses and such) such that it is clear to the read what they fence in, but not to such an extend that the fences dominate the expression. Dec 20, 2011 at 12:36
• @MarkS.Everitt I disagree with this comment of yours "most of the times you won't need these" about the \big... family of commands. In fact, I personally believe that most of the times one shouldn't use the \left...\right construct; the family of \big... commands produces much better spacing (both vertically and horizontally) in most situations; besides you don't need to match them across lines in a display. Apr 12, 2013 at 20:19

Automatically sized parentheses are obtained with \left and \right, as any LaTeX guide or manual tells.

However, automatic sizing is not good in every case; one of these cases is precisely that of summations with limits above and below: compare the results of

$\left( \sum_{i=1}^{n-1} i \right)\biggl(\sum_{i=1}^{n-1} i\biggr)$ (the font is that obtained with \usepackage{fouriernc}). In general the second way is to be preferred.

• Do you have a reference explaining why the size is bad on the left sum? Feb 2, 2015 at 10:31
• @VincentGuillemot The TeXbook, for instance. Feb 2, 2015 at 10:54
• OK, thks. Let me rephrase my comment: the argument "it's prettier" (used in the TeXBook) leaves me a little bit disappointed. Isn't there a more substantial reason hidden behind this aspiration to prettyness? Feb 2, 2015 at 12:51
• I find the former to be prettier.
– JAB
Feb 2, 2016 at 15:42
• Prettier or not, sometimes some publications simply require the right style and then this answer comes so handy! However with today's MikTex I am getting File fouriernc.sty' not found. and it looks like just including the package is not enough. This file has to beinstalled manually.
– aiag
Feb 5, 2017 at 17:52

One way is using \left and \right, followed by the parenthesis you want to use. These are mostly () [] {} \langle\rangle and |. You can also use a . to have no parenthesis displayed, e.g. when you want an opening, but no closing one.

\left( \frac12 \right)
\left\langle \frac23 \right.
\left\{ \frac34 \right]


creates If you want to control the size manually, use (in ascending order) \big, \Big, \bigg, \Bigg.

( \frac12 \big)
\Bigg\langle \frac23 \big] • One should use \bigl in front of the left delimiter and \bigr in front of the right delimiter (similarly for \Bigl-\Bigr and the others). This is important for spacing. Dec 20, 2011 at 7:40
• @egreg: When should one use just plain \big and friends? i.e., without the l|r suffix? Dec 20, 2011 at 10:34
• \big and friends can go in front of ordinaries: \big/ or \big|. Dec 20, 2011 at 11:41
• @egreg at least as long as \big| is not a part of a pair: \big|-x\big|\neq \bigl|-x\bigr| Dec 20, 2011 at 12:34
• I was just looking for a way to adjust { size by the formula inclosed in it. I used \left{. your answer was great. it learned me to use \left\{` instead Aug 8, 2015 at 10:19