# Numerators and denominators in fractions at different height

I'm trying to write a rather lengthy equation with a fraction multiplied by another fraction that has several \left( and \right) brackets. The height of the symbols above the fraction line is two high in the second fraction. How can I fix this?

\rho_{MN} = \frac{b^2 M}{4\pi} \frac{aR^2+\left[a + 3    \sqrt{z^2+b^2}\right]\left[a+\sqrt{z^2+b^2}\right]^2}{\left\{ R^2+ \left[a+\sqrt{z^2+b^2}\right]^2\right\}^{5/2}\left(z^2+b^2\right)^{3/2}}


• Why do you use \frac{•}{•} two times and not just one single \frac{•}{•}: \rho_{MN} = \frac{b^2 MaR^2+\left[a + 3 \sqrt{z^2+b^2}\right]\left[a+\sqrt{z^2+b^2}\right]^2}{4\pi\left\{ R^2+ \left[a+\sqrt{z^2+b^2}\right]^2\right\}^{5/2}\left(z^2+b^2\right)^{3/2}} – Benjamin Feb 11 '16 at 6:11
• To improve search capability, consider changing the title of your question to "Numerators in fractions at different height" or "Numerators and denominators in fractions at different height". I had never heard of the word "nominator" used in this context, but see at the following link that it is a rare (and maybe incorrect) usage. math.stackexchange.com/questions/159081/… – James Feb 11 '16 at 12:37
• @Benjamin Tha was how it was presented in the litterature, so I want to go with that format. – Espen Brun Feb 11 '16 at 16:20
• @James Changed it :) – Espen Brun Feb 11 '16 at 16:20
• @MWijnand You are right. I missed that. But that is actually imho a real problem with his notation. It is way too easy to miss the short break of the fraction line. There should be either brackets around the whole Numerator in the second fraction or at least a \cdot between the two fractions. – Benjamin Feb 11 '16 at 16:36

Personally, I would avoid using \left...\right and rather opt for specifying the delimiter sizes via \big-like options. In this specific instance, it suffices to use \bigl...\bigr sizes:

\documentclass{article}

\usepackage{amsmath}

\begin{document}

$\rho_{MN} = \frac{b^2 M}{4\pi} \frac{aR^2 + \left[ a + 3 \sqrt{z^2 + b^2} \right] \left[ a + \sqrt{z^2 + b^2} \right]^2} {\left\{ R^2 + \left[ a + \sqrt{z^2 + b^2} \right]^2 \right\}^{5/2} \left( z^2 + b^2 \right)^{3/2}}$

$\rho_{MN} = \frac{b^2 M}{4\pi \vphantom{\big(^{/}}} \frac{aR^2 + \bigl( a + 3 \sqrt{z^2 + b^2}\, \bigr) \bigl( a + \sqrt{z^2 + b^2}\, \bigr)^2} {\bigl( R^2 + \bigl(a + \sqrt{z^2 + b^2}\, \bigr)^2 \bigr)^{5/2} \bigl( z^2 + b^2 \bigr)^{3/2}}$

\end{document}


The correct placement of the denominator in the left-most fraction is obtained by using a \vphantom of the largest combination of items: a parenthesis together with a superscript - \bigl(^{/}.

• There should be \, between the square roots and the right delimiters, they're clashing into each other. – egreg Feb 11 '16 at 8:47
• @egreg: Great advice! – Werner Feb 11 '16 at 8:51
• Personally, I would use \big nowhere in this formula; adding ^{5/2\,} to the previous comment and removing all \bigl and \bigr I get this result – egreg Feb 11 '16 at 8:56
• @Werner Thanks, that fixed it! I didn't know about \big before this, but I will start using that now. – Espen Brun Feb 11 '16 at 16:16