Adjusting the Size of Summation Symbol inside an Enumerate Environment

Question

Situation: I am making a compilation of problems involving the summation symbol.

Problem: I want to resize my summation symbols but unable to do inside the enumerate environment even with the relsize package.

Question: Is there an alternative way to resize (i.e enlarge) the summation symbols? Also, does this apply to other math symbols (e.g., integrals)? Thank you.

EDIT: I forgot to mention that I already included the

\everymath{\displaystyle}

to my document. However, I would like to enlarge further the summation symbols beyond what \displaystyle could offer. Is there any way to do this? Any suggestion would be greatly appreciated.

Code :

\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage[includeheadfoot,footskip=0in,paperheight=11in,paperwidth=8.5in,left=1in,right=0.5in,top=0.7in,bottom=0.5in,]{geometry}
\usepackage{amsmath, amsfonts, amssymb, amsxtra, fancyhdr}
\usepackage{graphicx, parskip, xcolor, url, enumerate}
\usepackage{amsbsy, amstext, amsthm, relsize}


%Commands
\newcommand\sumone{\sum\limits_{n=1}^{+\infty}}
\newcommand\sumzero{\sum_{n=0}^{+\infty}}
\newcommand\sumtwo{\sum\limits_{n=2}^{+\infty}}


 \begin{document}
 Determine whether the following given items are absolutely convergent, conditionally convergent or divergent.

 \setlength\columnsep{-1.3cm}

   \begin{multicols}{4}
   \begin{enumerate}[a.]

   \item $\sumzero \cfrac{2n - 1}{n+3}$
   \item $\sumone \frac{\raisebox{0.15ex}{$6n^2 - 9n + 4$}}{n^3}$
   \item $\sumone \dfrac{3n - 2n^2}{n^2+1}$
   \item $\sumone \dfrac{2 + \sin n}{4+n^2}$
   \item $\sumone \dfrac{2n}{n^{3/2} +2}$
   \item $\sumone \dfrac{(-1)^n}{\sqrt{n+n^2}}$
   \item $\sumone \dfrac{n}{n+1}$
   \item $\sumone \dfrac{n + \sqrt{n}}{n^3 + 1}$
   \item $\sumtwo \dfrac{1}{n\sqrt{\ln n}}$
   \item $\sumone \left(\dfrac{2}{n\sqrt{n}} + \left( \dfrac{-4}{3} \right)^n\right)$

   \end{multicols}
   \end{enumerate}
   \end{document}

Answer 1

By "resizing" the summation symbols, I assume you want to enlarge them, so that they have the size used in display-math environments. This may be achieve most directly by placing \displaystyle directives ahead of \sum macros that occur in inline-math environment.

This works for \int, \prod, and other so-called variable-sized operator symbols as well.

Having to remember to type \displaystyle at the start of lots of inline math groups is tedious. To make all inline-math instances behave according to \displaystyle, provide the instruction \everymath{\displaystyle} at the start of the environment of interest -- here: an enumerate environment.

\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage[includeheadfoot,footskip=0in,letterpaper,
            left=1in,right=0.5in,top=0.7in,bottom=0.5in,
           ]{geometry}
\usepackage{amsmath, enumerate, multicol}

%Commands
\newcommand\sumone{\sum_{n=1}^{\infty}}
\newcommand\sumzero{\sum_{n=0}^{\infty}}
\newcommand\sumtwo{\sum_{n=2}^{\infty}}

\begin{document}
Determine whether the following given items are absolutely convergent, 
conditionally convergent, or divergent.

\setlength\columnsep{-1cm}

\begin{multicols}{4}
\begin{enumerate}[a.]
\everymath{\displaystyle}  % <-- new!
\item $\sumzero\frac{2n - 1}{n+3}$  % I wouldn't use "\cfrac"
\item $\sumone \frac{6n^2 - 9n + 4}{n^3}$ % I removed the "\raisebox" wrapper
\item $\sumone \frac{3n - 2n^2}{n^2+1}$
\item $\sumone \frac{2 + \sin n}{4+n^2}$
\item $\sumone \frac{2n}{n^{3/2} +2}$
\item $\sumone \frac{(-1)^n}{\sqrt{n+n^2}}$
\item $\sumone \frac{n}{n+1}$
\item $\sumone \frac{n + \sqrt{n}}{n^3 + 1}$
\item $\sumtwo \frac{1}{n\sqrt{\ln n}}$
\item $\sumone \left(\frac{2}{n\sqrt{n}} + 
               \left(\frac{-4}{3}\right)^{\!\!n}\,\right)$

\end{enumerate}
\end{multicols}
\end{document}