# brackets in equations

How do I make the fraction in this equation sit in the middle of the big brackets?

\documentclass{article}
\usepackage{amsmath}
\begin{document}

$T = \ln \left (\frac{\displaystyle\frac{\displaystyle\left( x \times y \right)^{z}}{\displaystyle\left( \left(R \right)^{z} \times A \right)}}B} \right )$
\end{document}

• please always post a complete small document that we can run to see the problem, but why all the \displaystyle? it should almost never be used. – David Carlisle Nov 3 '18 at 20:54
• the centre of the brackets and the fraction line are aligned with the = so if you have a large numerator or large denominator the will be space inside the brackets. – David Carlisle Nov 3 '18 at 20:56
• Sure, I will remember for next time. A friend made the equation for me, but I can edit it. – dragoness24 Nov 3 '18 at 21:04
• Why not simplifying the notation: $T = \ln\left(\frac{(x \times y)^z}{B(R^z \times A)}\right)$? – user94293 Nov 3 '18 at 21:06

## 4 Answers

Perhaps this is what you want?

\documentclass{article}
\usepackage{amsmath}

\begin{document}

$T = \ln \begin{pmatrix}\!\dfrac{\dfrac{\left( x \times y \right)^{z}}{\displaystyle\left( \left(R \right)^{z} \times A \right)}} {B}\!\end{pmatrix}$

\end{document} • Thanks! This is what I would like. If I want to use this in the \begin{equation} \end{equation} environment, how do I write it out? – dragoness24 Nov 3 '18 at 21:20
• Exactly the same way, except that you use the equation environment instead of $...$. – Bernard Nov 3 '18 at 21:23
• This will make readers scratch their heads in trying to guess what's the main fraction line. – egreg Nov 3 '18 at 22:08
• @egreg: One can easily make the main fraction line a little longer, or use \mfrac for the fraction in the numerator. – Bernard Nov 3 '18 at 22:12 You can re-arrange so it is less tall

\documentclass{article}
\usepackage{amsmath}
\begin{document}

orig
$T = \ln \left (\frac{\displaystyle\frac{\displaystyle\left( x \times y \right)^{z}}{\displaystyle\left( \left(R \right)^{z} \times A \right)}}B} \right )$

aa
$T = \ln \left (\dfrac{1}{B}\dfrac{(x \times y)^{z}}{(R^{z} \times A)} \right )$

\end{document}

• Thanks! In the form of equation I have to write in my thesis, 1/B is not used so I have to have a bigger equation. – dragoness24 Nov 3 '18 at 21:06
• @dragoness24 then I would accept the extra space, lowering the fraction so the main bar is not aligned with the = makes it confusing and hard to see which is the outer fraction. Either the form here or the second form in the other answer avoid that problem. – David Carlisle Nov 3 '18 at 21:12

While not recommending exactly this, you can center the term inside the outer parens using vcenter like this:

$T = \ln \left( \vcenter{\hbox{ \dfrac{\dfrac{\left( x \times y \right)^{z}}{\left( \left(R \right)^{z} \times A \right)}}{B} }}\right )$ There exist, however, much better solutions like the following simple formulation:

$T = \ln \left( \frac{( x \times y)^z / ( (R)^z \times A )}{B} \right )$

• Thanks! If it's within a \begin{equation} \end{equation} environment, I just have to omit the [ and ] and the \$ ? – dragoness24 Nov 3 '18 at 21:04

The simplest workaround is omitting the big parentheses: \log x has been considered the same as \log(x) for a few centuries and it continues to be. If the argument to the logarithm is a fraction, there's no doubt whatsoever what the logarithm applies to.

Thus type

\ln\frac{\dfrac{( x \times y)^{z}}{( (R)^{z} \times A )}}{B}


with no \left and \right, which serve no purpose here. Also the \displaystyle declarations are useless (and also a bit wrong).

Lowering the big fraction to get smaller parentheses is wrong: it will make very unclear what the main fraction line is. Beware that A/(B/C) is AC/B, whereas (A/B)/C is A/(BC), quite different things. Having \ln aligned with the middle row in the three story fraction will generate doubts in your readers. The fact one line is slightly longer than the other will not help at all: have mercy of your readers with weak sight. Multiple story fractions are never interpreted “top to bottom”:

    A
–
B
x = –
C
–
D


is interpreted as AD/BC and not as ((A/B)/C)/D which is A/(BCD). The position of the main fraction line on the formula axis makes the meaning clear.

This said, choose between the three following proposal: as usual in the order good, bad and ugly from top to bottom.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

$\ln\left(\frac{1}{B}\frac{( x \times y)^{z}}{R^{z} \times A}\right)$

$\ln\frac{\dfrac{( x \times y)^{z}}{R^{z} \times A}}{B}$

$\ln\left( \begin{gathered} \frac{\;\dfrac{( x \times y)^{z}}{R^{z} \times A}\;}{B} \end{gathered} \right)$

\end{document} 