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 don't want
$
inside\begin{equation}
\left{
is illegal; you want to have a growing brace and the command for printing an 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: