The code below produces the error

Missing delimiter (. inserted).

```
{\it \begin{equation}
$E_{k} = 10\log_{10}\left{ \frac{\sum_{i=1}^{M_{k}}{{\left[W_{k}^{P} x(i)\right]}^{2}}}{M_{k}}\right} (dB), \hspace{5em} k = 1,2,....,N\hspace{7em}$
\end{equation}}\\
```

## Best Answer

Let me reformat your code to better understand what's wrong.

There is no need to have a group around the equation.

The command

`\it`

does nothing useful and, besides, it has been deprecated for twenty yearsYou

wantdon't`$`

inside`\begin{equation}`

`\left{`

is illegal; you want to have a growing brace and the command forprintingan open brace is`\{`

You seem to have lost the count of braces, due to the fraction. You probably wanted

(note that

`\left[`

and`\right]`

are not necessary, they're even bad!)`\right}`

is similar to the above.ellipsis should be denoted by

`\dots`

The final

`\hspace{7em}`

serves no purposeSo, here's a better realization

You probably also want to use

`siunitx`

for units, so`\,\mathrm{dB}`

can better become`\si{\decibel}`

, which is even much clearer, isn't it?The fraction appears to be quite crowded, though; better set the denominator in front of the summation: