What's wrong with this?
\begin{equation}
\partial{Q}=\frac{1}{2}\frac{\sum{h_f}}{\sum \left({\frac{h_{fi}}{Q_i}\right)}}
\end{equation}
I keep getting errors.
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Sign up to join this communityMake sure that you have put the curlybraces at the correct position. Also, the pair causing problems here, doesn't do anything here, so I suggest just removing it.
When there are lots of groups like {}
and such, It gets difficult to see the where each group begins and ends. Try to add some space between, to ease the reading. Spaces are ignored in math-mode, so you can use as much as you want.
I have added two suggestions on how you could make it easier to read. The first simply adds some single-spaces here and there, while the other one adds linebreaks and indentation. This is probably overkill fo this example, but for complex formulas and programming, it is really a must. Both of them produces the same ouput.
Output
Code
\documentclass[11pt]{article}
\usepackage{mathtools}
\begin{document}
\begin{equation}
\partial{Q} = \frac{1}{2} \frac{ \sum{h_f} }{ \sum \left( \frac{ h_{fi} }{ Q_i } \right)}
\end{equation}
\begin{equation}% Same code, just formated for ease of reading. Overkill.
\partial{Q} = \frac{1}{2}
\frac{
\sum{h_f} }{
\sum \left(
\frac{ h_{fi} }{ Q_i }
\right)
}
\end{equation}
\end{document}
}\right)
instead of\right)}
(in my opinion, the corresponding pair of braces isn't necessary).