Multiplication Formatting
It looks like he used array
, which is more or less the same as tabular
but in math mode. I would prefer it without all the spaces.
\documentclass{article}
\usepackage{booktabs}
\begin{document}
\begin{displaymath}
\begin{array}{*{5}{@{}r@{}}}
& & -3x^2 & {}+2x & {}-4\\
& \times & 5x^2 & & {}+3\\\midrule
& & -9x^2 & {}+6x & {}-12\\
-15x^4 & {}+10x^3 & {}-20x^2\\\midrule
-15x^4 & {}+10x^3 & {}-29x^2 & {}+6x & {}-12
\end{array}
\end{displaymath}
\end{document}
Here's another array
-based solution. The array
features a total of 9 columns: 5 columns for the powers of x
and 4 columns for the +
and -
symbols, which are thus vertically aligned with each other.
An \rlap
instruction is used to make the final .
(period) and the QED-symbol protrude beyond the right-hand edge of the array
.
\documentclass{article}
\usepackage{array} % for "\newcolumntype" macro
\usepackage{booktabs}% for "\midrule" macro
\usepackage{amsthm} % for "\qedsymbol" macro
\newcolumntype{C}{>{{}}c<{{}}}
\newcommand{\ltimes}{\multicolumn{1}{l}{\times}}
\begin{document}
\[
\setlength\arraycolsep{0pt}
\renewcommand\arraystretch{1.5}
\begin{array}{*{4}{rC}r}
& & & - & 3x^2 & + & 2x & - & 4 \\
& &\ltimes& & 5x^2 & & & + & 3 \\
\midrule
& & & - & 9x^2 & + & 6x & - & 12\\
-15x^4 & + & 10x^3 & - & 20x^2 \\
\midrule
-15x^4 & + & 10x^3 & - & 29x^2 & + & 6x & - & 12\rlap{.\quad\qedsymbol}\\
\end{array}
\]
\end{document}
I propose another solution, based on alignedat
:
\documentclass{article}
\usepackage{booktabs}
\usepackage{mathtools}
\begin{document}
\[ \begin{array}{@{}c@{}}
\begin{alignedat}{5}
& & & & -3&x^2 & {}+2&x & {}-4& \\
& & & &{}\times 5&x^2 & & & {}+3 & \\\midrule[0.4pt]
& & & & -9 & x^2 & {}+6 &x & {}-12& \\
-15 & x^4 & {}+10 & x^3 &{}-20 & x^2\\\midrule[0.4pt]
-15 & x^4 & {}+10 & x^3 & {}-29&x^2 & {}+6 &x & {}-12&
\end{alignedat}
\end{array} \]
\end{document}