# Cancel out factorial fractions

I have the following fraction: How can I use a line and cross off the 3, 2, and 1s in the numerator and denominator?

I need a line crossing off the 3s in the numerator and denominator - one line. Same goes for 2s and 1s. (not two separate lines in numerator and denominator).

• Should this be done automatically? – user31729 May 9 '16 at 22:23
• Have you looked at this answer? It seems to do what you want. – Jānis Lazovskis May 9 '16 at 22:26
• @jlv i need to cross out individual numbers between the numerator and denominator – MCMastery May 9 '16 at 22:28

Simple with pst-node: define the numbers you want to cancel as nodes, and connect the corresponding nodes with a line:

\documentclass{article}

\usepackage{mathtools}
\usepackage{pst-node}
\usepackage{auto-pst-pdf}

\begin{document}

$\begin{pspicture} \dfrac{7\cdot 6\cdot 5\cdot 4\cdot\Rnode{n3}{3}\cdot\Rnode{n2}{2}\cdot\Rnode{n1}{1}}% {\Rnode{d3}{3}\cdot\Rnode{d2}{2}\cdot\Rnode{d1}{1}} \psset{linewidth=0.3pt, nodesep=-6pt} \ncline[linecolor=magenta]{n3}{d3} \ncline[linecolor=cyan]{n2}{d2} \ncline[linecolor=green]{n1}{d1} \end{pspicture}$

\end{document} 