\documentclass[20pt, reqno]{amsart}
\usepackage[margin=1in]{geometry}
\geometry{letterpaper}
%\geometry{landscape} % Activate for for rotated page geometry
\usepackage[parfill]{parskip} % Activate to begin paragraphs with an empty line rather than an indent
\usepackage{amsfonts, amscd, amssymb, amsthm, amsmath}
\usepackage{pdfsync} %leaves makers for tex searching
\usepackage{enumerate}
\usepackage[pdftex,bookmarks]{hyperref}
\usepackage[utf8]{inputenc}
\usepackage{graphicx}
\usepackage{setspace}
\usepackage[mathscr]{euscript}
%%% Theorems %%%---------------------------------------------------------
\doublespacing
%%% Environments %%%---------------------------------------------------------
\newenvironment{ans}{\medskip \paragraph*{\emph{Answer}.}}{\hfill \break $~\!\!$ \dotfill \medskip }
\newenvironment{sketch}{\medskip \paragraph*{\emph{Proof sketch}.}}{ \medskip }
\newenvironment{summary}{\medskip \paragraph*{\emph{Summary}.}}{ \hfill \break \rule{1.5cm}{0.4pt} \medskip }
\newcommand\Ans[1]{\hfill \emph{Answer:} {#1}}
\usepackage{tikz}
\usepackage{pgfplots}
\usepackage{color}
\newcommand{\NOTE}[1]{{\color{blue}#1}}
\newcommand{\MOVED}[1]{{\color{gray}#1}}
%%% Alphabets %%%---------------------------------------------------------
%%% Some shortcuts for my commonly used special alphabets and characters.
\def\cA{\mathcal{A}}\def\cB{\mathcal{B}}\def\cC{\mathcal{C}}\def\cD{\mathcal{D}}\def\cE{\mathcal{E}}\def\cF{\mathcal{F}}\def\cG{\mathcal{G}}\def\cH{\mathcal{H}}\def\cI{\mathcal{I}}\def\cJ{\mathcal{J}}\def\cK{\mathcal{K}}\def\cL{\mathcal{L}}\def\cM{\mathcal{M}}\def\cN{\mathcal{N}}\def\cO{\mathcal{O}}\def\cP{\mathcal{P}}\def\cQ{\mathcal{Q}}\def\cR{\mathcal{R}}\def\cS{\mathcal{S}}\def\cT{\mathcal{T}}\def\cU{\mathcal{U}}\def\cV{\mathcal{V}}\def\cW{\mathcal{W}}\def\cX{\mathcal{X}}\def\cY{\mathcal{Y}}\def\cZ{\mathcal{Z}}
\def\AA{\mathbb{A}} \def\BB{\mathbb{B}} \def\CC{\mathbb{C}} \def\DD{\mathbb{D}} \def\EE{\mathbb{E}} \def\FF{\mathbb{F}} \def\GG{\mathbb{G}} \def\HH{\mathbb{H}} \def\II{\mathbb{I}} \def\JJ{\mathbb{J}} \def\KK{\mathbb{K}} \def\LL{\mathbb{L}} \def\MM{\mathbb{M}} \def\NN{\mathbb{N}} \def\OO{\mathbb{O}} \def\PP{\mathbb{P}} \def\QQ{\mathbb{Q}} \def\RR{\mathbb{R}} \def\SS{\mathbb{S}} \def\TT{\mathbb{T}} \def\UU{\mathbb{U}} \def\VV{\mathbb{V}} \def\WW{\mathbb{W}} \def\XX{\mathbb{X}} \def\YY{\mathbb{Y}} \def\ZZ{\mathbb{Z}}
\def\fa{\mathfrak{a}} \def\fb{\mathfrak{b}} \def\fc{\mathfrak{c}} \def\fd{\mathfrak{d}} \def\fe{\mathfrak{e}} \def\ff{\mathfrak{f}} \def\fg{\mathfrak{g}} \def\fh{\mathfrak{h}} \def\fj{\mathfrak{j}} \def\fk{\mathfrak{k}} \def\fl{\mathfrak{l}} \def\fm{\mathfrak{m}} \def\fn{\mathfrak{n}} \def\fo{\mathfrak{o}} \def\fp{\mathfrak{p}} \def\fq{\mathfrak{q}} \def\fr{\mathfrak{r}} \def\fs{\mathfrak{s}} \def\ft{\mathfrak{t}} \def\fu{\mathfrak{u}} \def\fv{\mathfrak{v}} \def\fw{\mathfrak{w}} \def\fx{\mathfrak{x}} \def\fy{\mathfrak{y}} \def\fz{\mathfrak{z}}
\def\fgl{\mathfrak{gl}} \def\fsl{\mathfrak{sl}} \def\fso{\mathfrak{so}} \def\fsp{\mathfrak{sp}}
\def\GL{\mathrm{GL}} \def\SL{\mathrm{SL}} \def\SP{\mathrm{SL}}
\def\<{\langle} \def\>{\rangle}
\usepackage{mathabx}
\def\acts{\lefttorightarrow}
\def\ad{\mathrm{ad}}
\def\Aut{\mathrm{Aut}}
\def\Ann{\mathrm{Ann}}
\def\dim{\mathrm{dim}}
\def\End{\mathrm{End}}
\def\ev{\mathrm{ev}}
\def\half{\hbox{$\frac12$}}
\def\Hom{\mathrm{Hom}}
\def\id{\mathrm{id}}
\def\sgn{\mathrm{sgn}}
\def\Tor{\mathrm{Tor}}
\def\tr{\mathrm{tr}}
\def\vep{\varepsilon}
\def\f{\varphi}
\pgfplotsset{compat = newest}
\title{Practice problem Set for Midterm II part 1}
\begin{document}
\maketitle
\begin{enumerate}[Q1]
\item Solve the linear system using whatever method you like
\begin{equation}
\left\{
\begin{aligned}
x-4y=4 \nonumber
\\3x+2y=7 \nonumber
\end{aligned} \right
\end{equation}
\item
\end{enumerate}
\end{document}
我得到的错误是在 \end{enumerate} 处发现未封闭的 \begin{equation} 但是我结束了等式。
答案1
- 请始终提供可重现问题的 MWE（最小工作示例）。大多数前言代码与其无关。
- 您的问题已通过@slurp 评论解决
- 因此，这里添加了一些题外的建议，如何简化方程式的编写。您可能会发现它们很有用：
- 对齐环境需要与符号，方程式与之对齐
- 而不是
\nonumbers˛at each equation you rathe use[ ... ]or\begin{equation*} ... \end{equation*}`
\documentclass[20pt, reqno]{amsart}
\usepackage[letterpaper,
margin=1in]{geometry}
\usepackage{amsmath, amscd, amssymb, amsthm,}% amsfonts is loaded by amssymb
\usepackage{enumerate}
\begin{document}
\begin{enumerate}[Q1]
\item Solve the linear system using whatever method you like
\[ % or \begin{equation*} ... \end{equation*}
\left\{
\begin{aligned}
x-4y & = 4 \\
3x+2y & = 7
\end{aligned} \right.
\]
\item \dots
\end{enumerate}
\end{document}
