# Cross Multiplication with Arrows

I am trying to find help on how to reproduce the following image. I don't have much for a minimal example except:

\documentclass{article}
\usepackage{amsmath,mathtools}
\begin{document}
\begin{align*}
\dfrac{3}{5}&=\dfrac{4.50}{x}\\
3x&=5(4.50) &&\textcolor{blue}{\text{Set cross products equal}}
\end{align*}
\end{document}


Here is an image of what I want:

Can someone help?

Here is a proposal. Normally one could get rid of the darker region at the intersection by dialing transparency group, but for some reason this makes here the arrows disappear.

\documentclass{article}
\usepackage{amsmath,mathtools}
\usepackage{tikz}
\usetikzlibrary{tikzmark,calc,shapes.arrows}
\begin{document}
\begin{align*}
\tikzmark{f1}\dfrac{3}{5}&=\dfrac{4.50}{x}\tikzmark{f2}\\
3x&=5(4.50) &&\textcolor{blue}{\text{Set cross products equal}}
\end{align*}
\begin{tikzpicture}[overlay,remember picture]
\begin{scope}[opacity=0.2]
\begin{scope}[blend mode=multiply]
\path let
\p1=($([yshift=4mm,xshift=3mm]pic cs:f2)-([yshift=-2mm,xshift=-3mm]pic cs:f1)$),
\n1={veclen(\x1,\y1)} in
([yshift=-2mm,xshift=-3mm]pic cs:f1) -- ([yshift=4mm,xshift=3mm]pic cs:f2)
node[fill=blue,midway,sloped,single arrow,minimum height=\n1]{};
\path let
\p1=($([yshift=4mm,xshift=-3mm]pic cs:f1)-([yshift=-2mm,xshift=3mm]pic cs:f2)$),
\n1={veclen(\x1,\y1)} in
([yshift=-2mm,xshift=3mm]pic cs:f2) -- ([yshift=4mm,xshift=-3mm]pic cs:f1)
node[fill=blue,midway,sloped,single arrow,minimum height=\n1,
shape border rotate=180]{};
\end{scope}
\end{scope}
\end{tikzpicture}
\end{document}


• that is very good. Would placing the tikzmarks in denominators improve the picture? Let me look at this in the morning. Thank you. Again I would have never been able to come even close to this program. Way beyond my abilities. – MathScholar Oct 17 '18 at 2:53
• @MathScholar In this case it would probably be easier to adjust the yshift and xshift values. – user121799 Oct 17 '18 at 2:58
• is it possible to put text near the arrow tips without touching the arrows and disrupting the picture? – MathScholar Oct 19 '18 at 20:54
• Yes, just add nodes in the overlay picture. (I'm not really online now.) – user121799 Oct 19 '18 at 21:26
• I tried a few things but could not get it to work. I'd appreciate it if you show me later. No hurry, thanks Marmot – MathScholar Oct 19 '18 at 21:32