Arrow drawn to \tikzmark node inside \sqrt goes off the page

Question

This is my code:

\documentclass[11pt]{amsart}
\usepackage{geometry}                % See geometry.pdf to learn the layout options. There are lots.
\geometry{a4paper}                   % ... or a4paper or a5paper or ... 
\usepackage{tikz}
\newcommand{\tikzmark}[2]{%
\tikz[remember picture,baseline=(#1.base)]
\node[text=black,anchor=center,inner sep=2pt] (#1) {#2};}

\begin{document}

  \begin{equation*}
   \begin{aligned}
    \tikzmark{wexponent}{Wurzelexponent} && \\[1em]
     \sqrt[{\tikzmark{nwex}{n}}]{\tikzmark{aradi}{a}} & = \tikzmark{xwter}{x} \\[1em] %radikand will nicht pfeilen-----------------
      \tikzmark{radikand}{Radikand} && \tikzmark{wterm}{Wurzelterm}\\[1em]
      (-2)^2 & =\sqrt[2]4\neq -2
    \end{aligned}
    \phantom{\hspace{88.5mm}}
  \tikz[overlay,remember picture]{\draw[blue,thick,->] (wexponent.south) to [bend left=0] node[anchor=south]{$ $}(nwex.north);}
  \tikz[overlay,remember picture]{\draw[blue,thick,->] (radikand.north) to [bend left=0] node[anchor=south]{$ $}(aradi.south);}
  \tikz[overlay,remember picture]{\draw[blue,thick,->] (wterm.north) to [bend left=0] node[anchor=south]{$ $}(xwter.east);}
  \end{equation*} 


\end{document}  

Why does this arrow from "Radikand" to inside of the base of the \sqrt go to the wrong place?

Answer 1

For some reason, your custom \tikzmark REALLY doesn't like being inside \sqrt. Using \sbox causes \tikzmark to execute outside \sqrt but be displayed inside. The change to tikzpicture outside the equation* isn't really necessary, but does reduce the number of \pgfsyspdfmark entries in the aux file.

\documentclass[11pt]{amsart}
\usepackage{geometry}                % See geometry.pdf to learn the layout options. There are lots.
\geometry{a4paper}                   % ... or a4paper or a5paper or ... 
\usepackage{tikz}
\newcommand{\tikzmark}[2]{%
\tikz[remember picture,baseline=(#1.base)]%
{\node[text=black,anchor=center,inner sep=2pt] (#1) {#2};}}

\begin{document}

  \begin{equation*}
   \begin{aligned}
    \tikzmark{wexponent}{Wurzelexponent} && \\[1em]
     \sbox1{\tikzmark{aradi}{a}}%
     \sqrt[{\tikzmark{nwex}{n}}]{\usebox1} & = \tikzmark{xwter}{x} \\[1em] %radikand will nicht pfeilen-----------------
      \tikzmark{radikand}{Radikand} && \tikzmark{wterm}{Wurzelterm}\\[1em]
      (-2)^2 & =\sqrt[2]4\neq -2
    \end{aligned}
    \phantom{\hspace{88.5mm}}
  \end{equation*} 
  \begin{tikzpicture}[overlay,remember picture]
    \draw[blue,thick,->] (wexponent.south) to [bend left=0] (nwex.north);
    \draw[blue,thick,->] (radikand.north) to [bend left=0] (aradi.south);
    \draw[blue,thick,->] (wterm.north) to [bend left=0] (xwter.east);
  \end{tikzpicture}

\end{document}  

---

If you are going to be doing this a lot, you might find the \mathtikzmark macro below useful.

\documentclass[11pt]{amsart}
\usepackage{geometry}                % See geometry.pdf to learn the layout options. There are lots.
\geometry{a4paper}                   % ... or a4paper or a5paper or ... 
\usepackage{tikz}
\newcommand{\tikzmark}[2]{%
\tikz[remember picture,baseline=(#1.base)]%
{\node[text=black,anchor=center,inner sep=2pt] (#1) {#2};}}

\usepackage{mathstyle}
\makeatletter
\newcommand{\mathtikzmark}[2]{%
\tikz[remember picture,baseline=(#1.base)]%
{\node[text=black,anchor=center,inner sep=2pt] (#1) {$\m@th\currentmathstyle#2$};}}
\makeatother

\begin{document}

  \begin{equation*}
   \begin{aligned}
    \tikzmark{wexponent}{Wurzelexponent} && \\[1em]
     \sbox1{\tikzmark{aradi}{$a$}}%
     \sqrt[{\mathtikzmark{nwex}{n}}]{\usebox1} & = \mathtikzmark{xwter}{x} \\[1em] %radikand will nicht pfeilen-----------------
      \tikzmark{radikand}{Radikand} && \tikzmark{wterm}{Wurzelterm}\\[1em]
      (-2)^2 & =\sqrt[2]4\neq -2
    \end{aligned}
    \phantom{\hspace{88.5mm}}
  \end{equation*} 
  \begin{tikzpicture}[overlay,remember picture]
    \draw[blue,thick,->] (wexponent.south) to [bend left=0] (nwex.north);
    \draw[blue,thick,->] (radikand.north) to [bend left=0] (aradi.south);
    \draw[blue,thick,->] (wterm.north) to [bend left=0] (xwter.east);
  \end{tikzpicture}

\end{document}