Changing size of parentheses using \left and \right

Question

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.

Answer 1

Make 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}