[Tex/LaTex] How to place texts “side by side”

Question

I want to create something like this:

The left hand side has the definition and right hand side we have examples. The left hand side and the right hand side could be simply separated by a "\qquad". But this is only at one particular location of the page, I don't want the entire page to be partitioned into two columns (as by using multicol)

The idea is sort of like subplot, or subfigure where you can place pictures side by side

Is this done through a table? Do we partition the page into two columns at a given location? What is the best way to achieve this?

Answer 1

Two side-by-side minipage environments will work. In the example below, the left-hand minipage is twice as wide as the one on the right; feel free to adjust the relative sizes to suit your needs.

\documentclass{article}
\usepackage{amsmath} % for "\text" macro
\begin{document}

\noindent
\begin{minipage}[t]{0.6667\textwidth}
\textbf{Root test}: 
Given $\displaystyle \sum_{n=1}^\infty \lvert a_n\rvert^{\frac{1}{n}}$ then:

\smallskip
1. $L>0 \Rightarrow \text{Divergent}$

2. $L<0 \Rightarrow \text{Convergent}$

3. $L=0 \text{ Undetermined}$
\end{minipage}% % leave no gap
\begin{minipage}[t]{0.3333\textwidth}
Divergent:

$\displaystyle \sum_{n=1}^\infty \frac{-12^n}{n}$

\bigskip
Convergent:

$\displaystyle \sum_{n=1}^\infty \frac{n^n}{3^{1+2n}}$
\end{minipage}

\end{document}