6

Thanks for stopping by and looking at my question.

I'm trying to format my homework like my professor has shown in his notes, but I don't know how to write the code to make it look like this (shown below).

Any help you might be able to provide would be much appreciated.

finding products

4

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.

enter image description here

\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}
1
  • Thank you, @Mico, I appreciate your time, your solution looks very nice!
    – jbrow35
    Nov 17 '16 at 21:09
4

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}

enter image description here

4
  • Thanks, @StefanH, that looks great! Yeah, I'm not sure why all the space in his, but yours looks good to me! :)
    – jbrow35
    Nov 17 '16 at 20:54
  • In rows 1 and 2, the final - and + symbols are out of alignment with the - symbols in rows 3 and 5, even though they're all binary operators. Is this intentional?
    – Mico
    Nov 17 '16 at 20:57
  • Thanks, @Mico, I didn't even notice the - and + being out of alignment.
    – jbrow35
    Nov 17 '16 at 21:05
  • @Mico The signs are not aligned. I have the whole term, including the sign, in one column. Then I preferred to align the x. To do this a bit better the signs should have their own columns.
    – StefanH
    Nov 17 '16 at 21:15
3

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}

enter image description here

1
  • Hello, @Bernard! The more ways the better, I appreciate you taking the time to answer! :)
    – jbrow35
    Nov 17 '16 at 21:15
3

With autoaligne and the help of a trick in https://tex.stackexchange.com/a/339525/4427

\documentclass{article}
\usepackage{autoaligne}

%% A trick for an empty delimiter
\newcommand{\makeempty}[1]{%
  \begingroup\lccode`~=`#1 \lowercase{\endgroup\def~}{\mathbin{\phantom{+}}}%
  \mathcode`#1="8000
}


\begin{document}

\[
\setlength{\medmuskip}{18mu}
\makeempty{V}
\definirseparateurs{\\}{+||-||V}{}
\autoaligne{
+- 3x^2 + 2x - 4 \\
V \times\hfill V 5x^2 ++ 3 \\
\noalign{\vspace{3pt}\hrule\vspace{3pt}}
+- 9x^2 + 6x - 12 \\
\-15x^4 + 10x^3 - 20x^2 \\
\noalign{\vspace{3pt}\hrule\vspace{3pt}}
\-15x^4 + 10x^3 - 29x^2 + 6x - 12
}
\]

\end{document}

enter image description here

If you want it more compact, remove the \setlength line:

enter image description here

Here's a more accurate rendering of the original.

\documentclass{article}
\usepackage{amsthm,array}

\begin{document}

\[
\setlength{\extrarowheight}{1ex}
\begin{array}{@{}rclcrcrclll}
&&& - & 3x^2 & + & 2x & - & 4 \\[1ex]
&& \times & & 5x^2 &&& + & 3 \\[1ex]
\cline{1-10}
&&& - & 9x^2 & + & 6x & - & 12 \\[1ex]
-15x^4 & + & 10x^3 & - & 20x^2 \\[1ex]
\cline{1-10}
-15x^4 & + & 10x^3 & - & 29x^2 & + & 6x & - & 12 && \qedsymbol
\end{array}
\]
\end{document}

enter image description here

4
  • Ah, so that's how my professor go all that space in there! I didn't think I liked it originally, but now it's growing on me. Thanks, @egreg!
    – jbrow35
    Nov 17 '16 at 21:40
  • @jbrow35 I don't think autoaligne was used, it's quite a new package. I suspect an array similar to Mico's.
    – egreg
    Nov 17 '16 at 21:42
  • Oh, okay. Yeah, I think he wrote these notes back in 2013.
    – jbrow35
    Nov 17 '16 at 21:43
  • @jbrow35 I added a possible way your professor used.
    – egreg
    Nov 17 '16 at 22:02

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