Adapting this MWE (adapted from this Simple speech bubbles, arrows or balloon like shapes in beamer) and using the math enviroment \ensuremath
\documentclass[12pt]{article}
\usepackage{amsmath,amssymb}
\usepackage{tikz}
\usetikzlibrary{calc,shapes.callouts}
\newcommand{\clouds}[2]{
\tikz[remember picture,baseline]{\node[anchor=base,inner sep=0,outer sep=0]%
(#1) {{\ensuremath{#1}}};\node[overlay,cloud callout,callout relative pointer={(-0.7cm,-0.2cm)},%
aspect=2.5,draw=green] at ($(#1.south)+(4.2cm,1cm)$) {\ensuremath{#2}};}%
}%
\begin{document}
\clouds{y'+xy=0}{\text{Being } \dfrac{y'}y=-x}
\end{document}
you can recreate your picture with the commands of LaTeX
. To fixed the cloud you should to see the coordinates ($(#1.south)+(4.2cm,1cm)$)
and callout relative pointer={(-0.7cm,-0.2cm)}
for the correct positioning that it is depends from the type of equation or list of equations.
todonotes
package would be suitable for this purpose? – Marijn Jul 4 '20 at 15:45