\documentclass{article}
\usepackage{tikz}
\usepackage[hmargin=3cm,showframe]{geometry}
\usetikzlibrary{tikzmark,arrows.meta}
\tikzset{
shorten <>/.style={shorten >= #1, shorten <= #1}
}
\begin{document}
\[
\int 4x^3 \sqrt{x^4-6}\;dx = \int \sqrt{x^4-6}\;\;4x^3\;
\tikzmarknode{left eq}{dx}
\hspace{2cm}
\tikzmarknode{right eq}{\int} \sqrt{u}\;du = \frac{2}{3} u^{3/2} +C =
\frac{2}{3} (x^4-6)^{3/2} +C
\]
\tikz[remember picture, overlay]
\draw[
-{Triangle[width=18pt,length=8pt]},
line width=10pt,
pink,
shorten <>=12pt
]
(left eq.east) -- (left eq.east-|right eq.west)
;
\end{document}