Trying to use \left. and \right. for equation formatting

Question

I am trying to format this equation so that it fits in a two-column format with brackets. It's too long at this point and spreads to two columns at this point...

Here is the original code...

 \begin{multline}
 \label{encusts}
 N_{n}(T) =  \sum_{x=0}^{\infty} [1 - F(x)^n] \\ 
 \quad \quad   =  \sum_{x=0}^{\infty}\left[1-\left(1-x! \binom{2 x}{x} \rho ^x (\rho +1)^{-2  x-1}_2\tilde{F}_1\left(1,x+\frac{1}{2};x+2;\frac{4 \rho }{(\rho +1)^2}\right)\right)^n].
 \end{multline}

Here is the code that I can't compile. I'm trying to use \right. and \left. to make sure the brackets on the second line with the summation can match the bracket on the third line...

 \begin{multline}
 \label{encusts}
  N_{n}(T) =  \sum_{x=0}^{\infty} [1 - F(x)^n] \\ 
  \quad \quad   =  \sum_{x=0}^{\infty}\left[1-\left(1-x! \binom{2 x}{x} \rho ^x (\rho +1)^{-2x-1} \right. \\
  \left. \, _2\tilde{F}_1\left(1,x+\frac{1}{2};x+2;\frac{4 \rho }{(\rho +1)^2}\right)\right)^n    \right].
  \end{multline}

Thanks for the help...

Answer 1

You cannot have a left matching a right on another line with a \\ between the two. Within each line of an equation, ensure each left and `right are paired.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
 \begin{multline}
    \label{encusts}
    N_{n}(T) =  \sum_{x=0}^{\infty} [1 - F(x)^n] \\ 
    \quad \quad   =  \sum_{x=0}^{\infty}\left[1-\left(1-x! \binom{2 x}{x} \rho ^x (\rho +1)^{-2x-1} \right. \right. \\
    \left. \left.\, _2\tilde{F}_1\left(1,x+\frac{1}{2};x+2;\frac{4 \rho }{(\rho +1)^2}\right)\right)^n    \right].
\end{multline}\end{document}

which gives

I think you can improve the alignment further, but this at least solves the brackets.