Here is something that should get you started on using tikzmark:



Notes:


This does require two runs. First one to determine the locations, and the second to do the drawing.
There probably are easier ways to determine the locations.


Code:

\documentclass{article}

\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{calc}

\newcommand{\mytikzmark}[1]{\tikz[remember picture] \node[baseline, inner sep=0pt] (#1) {};}

\begin{document}

\begin{equation*}
 \sqrt{\frac{N\mytikzmark{top}}{p(1-p)\mytikzmark{bottom}}}
\end{equation*}
\begin{tikzpicture}[remember picture, overlay]
    \coordinate (Top Start)  at ([yshift=0.25\baselineskip]top -| bottom);
    \coordinate (Bottom End) at ([yshift=0.2\baselineskip]bottom);
    \draw [latex-latex, red, thick] 
            (Top Start) to[out=-5, in=5, distance=0.75cm] 
            (Bottom End);
    \node (MidHeight) at (Top Start |- Bottom End) {};
    \node  at ([shift={(1.5cm,0.5\baselineskip)}]Bottom End) (OTIMES) {$\otimes$};
    \draw [blue, -stealth, thick] (OTIMES) -- ++(-0.8cm,0);
\end{tikzpicture}%
\end{document}


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