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Parentheses around mismatched size fractions in LaTeX 
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#1
Apr2912, 05:43 PM

P: 1

I have a fraction in the denominator of another fraction, and I'm trying to put a set of brackets around it. However, I can't seem to get them to size properly. Example below:
\begin{equation} Q_1 \left[ \frac{Q_2}{4\pi \left( r_2+\sqrt{ \dfrac{Q_2\gamma A}{4\pi}} \right)^2 } +Q_3\right] \end{equation} Obviously, I want to get rid of the space at the top. I've tried using \Bigg[ (which ends up too small) and even creating my own sizing in the preamble:



#2
May212, 09:17 PM

Engineering
Sci Advisor
HW Helper
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P: 7,111

You can get the brackets right by putting the fraction inside a matrix.
That leaves the ##Q_1## in a silly place, but you can fix that with the \vphantom{} command. \vphantom{} works out the vertical height of what is inside the {}, and creates an invisible zerowidth object of that size. So, in front of the matrix in [ ] , make another matrix without backets, use \vphantom to make it the same height, and the ##Q_1## will line up with the ##Q_3##.
\vphantom{\frac{Q_2}{4\pi \left( r_2+\sqrt{ \dfrac{Q_2\gamma A}{4\pi}} \right)^2 }} Q_1 \end{matrix} \begin{bmatrix} \frac{Q_2}{4\pi \left( r_2+\sqrt{ \dfrac{Q_2\gamma A}{4\pi}} \right)^2 } + Q_3 \end{bmatrix}$$ if you are a perfectionist, you might want to put a bit of negative space in between the two matrices as well. Easy peasy. 


#3
May212, 10:54 PM

Mentor
P: 15,150

[tex]Q_1 \left[ \frac{Q_2}{4\pi \left( r_2+\sqrt{ \frac{Q_2\gamma A}{4\pi}} \right)^2 } + Q_3 \right][/tex] There are other ways to represent division. Sometimes [itex]a/b[/itex] looks better than [itex]\frac a b[/itex]: [tex]Q_1 \left[ \frac{Q_2}{4\pi \left( r_2+\sqrt{ (Q_2\gamma A)/(4\pi)} \right)^2 } + Q_3 \right][/tex] You can pull the [itex]4\pi[/itex] inside the parentheses as [itex]\sqrt{4\pi}[/itex]. This clears the denominator that is the root cause of your problems: [tex]Q_1 \left[ \frac{Q_2}{\left( r_2\sqrt{4\pi}+\sqrt{Q_2\gamma A} \right)^2 } + Q_3 \right][/tex] Sometimes \left and \right are too big. This is one of those times. Use \bigl and \bigr instead: [tex]Q_1 \left[ \frac{Q_2}{\bigl( r_2\sqrt{4\pi}+\sqrt{Q_2\gamma A} \bigr)^2 } + Q_3 \right][/tex] 


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