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}
\sqrt[x][{y}
uses\mathpalette
. This typesets the contents four times but only leaves the correct instance in the document. This might break your code here.