\documentclass[11pt]{article}
\usepackage{physics}
\usepackage{blindtext}
\usepackage{amsmath}
\usepackage{bm}
\usepackage{cancel}
\usepackage{sidecap}
\usepackage{array}
\usepackage[utf8]{inputenc}
\usepackage{enumerate}
\title{}
\author{Author:\\ \hfill\\ Registration Number: }
\date{Date:}
\begin{document}
\maketitle
\section{}
\subsection{}
\begin{enumerate}[i.]
\item my text
\item my text
\item my text
\noindent\rule{12.6cm}{0.7pt}
\item
\begin{equation}
\frac{y[n]}{x[n]} = \frac{1}{2}
\end{equation}
\item
\end{enumerate}
\end{document}
This is the outline of the document but I'm getting the error "missing $ inserted ... $". I've never had a problem with using the equations before so any help would be appreciated.
equationenvironment. Remove them and you'll be fine. We've had this before. – Werner Oct 31 '18 at 17:29alignenvironment – Werner Oct 31 '18 at 17:30alignandequationenvironment do not tolerate empty lines?; Blank lines in an equation and some other similar function – Werner Oct 31 '18 at 17:31