Indent doesn’t work inside enumerate enviroment

Question

I don't know why the 2nd line here is not indented. Have I loaded a package that overrides indentation? It seems not to work inside an enumerate enviroment.

\documentclass[12pt]{article}

\usepackage[utf8]{inputenc}
\usepackage{fullpage}
\usepackage{amsfonts}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{graphicx}
\usepackage[backend=biber, isbn=false, doi=false]{biblatex-chicago}

\newtheorem{lem}{Lemma}
\newtheorem{ex}{Example}

\newcommand{\Q}{\mathbb{Q}}
\newcommand{\Z}{\mathbb{Z}}
\newcommand{\N}{\mathbb{N}}
\newcommand{\R}{\mathbb{R}}
\newcommand{\C}{\mathbb{C}}

\DeclareMathOperator{\lcm}{lcm}
\DeclareMathOperator{\ord}{ord}

\title{Homework 2 - MATH 4001}
\author{Clyde Kertzer}
\date{\today}

\begin{document}

\setlength{\abovedisplayskip}{5pt}
\setlength{\belowdisplayskip}{5pt}
\setlength{\abovedisplayshortskip}{0pt}
\setlength{\belowdisplayshortskip}{0pt}

\setlength{\parindent}{20pt}

\maketitle
\begin{enumerate}
\item[2.] Show that the sequence of functions
$$ f_n(x)=\frac{n x}{1+n x} $$ 
does not converge uniformly on $[0,1]$.

Paragraph 2 (Why no indent)?

Answer 1

That's the standard behavior in LaTeX. Whenever a list is opened, \listparindent is set to zero. A similar behavior have minipage and \parbox.

If you want to have a different parindent in lists, you have to specify it and the simplest way is to use enumitem.

\documentclass[12pt]{article}

\usepackage{enumitem}

\setlist[enumerate]{listparindent=\parindent}

\begin{document}

\begin{enumerate}
\item Show that the sequence of functions
\[
f_n(x)=\frac{n x}{1+n x}
\]
does not converge uniformly on $[0,1]$.

Paragraph 2 (Why no indent)?

\end{enumerate}

\end{document}