中心和框列出带有公式的列表

Question

我正在尝试将“定积分的性质”子部分下的公式居中并框起来；但是，框并没有包裹住公式，而是向右延伸了一点，我无法将其居中。我尝试使用，\begin{center}但\end{center}可惜没有用。有人能给点建议吗？我附上了一张照片供参考。

\documentclass{article}
\usepackage{gensymb}
\usepackage{graphicx}
\usepackage[fleqn]{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage[usenames,dvipsnames]{color}
\usepackage{fullpage}
\usepackage{cancel}
\usepackage{easylist}
\usepackage{graphicx}
\usepackage{tikz}
\usepackage{framed} 
\usepackage{tcolorbox}
\begin{document}
\section{Integrals}
\subsection{Integral Properties \& Formulas}
\subsubsection{Properties of Definite Integrals}
\begin{framed}
\begin{itemize}
\item[I.] $\displaystyle{\int_a^b k\,dx=k(b-a)}$ 
\item[II.] $\displaystyle{\int_a^b k\cdot f(x)dx=k\cdot \int_a^b f(x)dx}$ 
\end{itemize}
\end{framed}
\end{document}

Answer 1

以下是两个可能的选择：

\documentclass{article}
\usepackage[fleqn]{amsmath}
\usepackage{framed,varwidth}
\begin{document}
\section{Integrals}
\begin{framed}
  \begin{itemize}
    \item[I.]  $\displaystyle \int_a^b k \mathrm{d}x = k(b - a)$
    \item[II.] $\displaystyle \int_a^b k \cdot f(x) \mathrm{d}x = k \cdot \int_a^b f(x) \mathrm{d}x$
  \end{itemize}
\end{framed}

\begin{center}
  \fbox{\quad%
    \begin{varwidth}{\linewidth}
      \begin{itemize}
        \item[I.]  $\displaystyle \int_a^b k \mathrm{d}x = k(b - a)$
        \item[II.] $\displaystyle \int_a^b k \cdot f(x) \mathrm{d}x = k \cdot \int_a^b f(x) \mathrm{d}x$
      \end{itemize}
    \end{varwidth}%
  \quad}
\end{center}

\begin{center}
  $\begin{array}{|@{\quad}rl@{\quad}|}
    \hline 
    & \\
    \text{I.}  & \displaystyle \int_a^b k \mathrm{d}x = k(b - a) \\
    \text{II.} & \displaystyle \int_a^b k \cdot f(x) \mathrm{d}x = k \cdot \int_a^b f(x) \mathrm{d}x \\
    & \\
    \hline
  \end{array}$
\end{center}

\end{document}

第一个使用\fboxedvarwidth环境，而第二个框是常规的array。

Answer 2

您可以使用empheq：

\documentclass{article}
\usepackage[fleqn]{amsmath}
\usepackage{empheq}

\newcommand{\diff}{\mathop{}\!\mathrm{d}}
\newenvironment{boxedalign}
 {\setlength\mathindent{0pt}%
  \empheq[box=\fbox]{align*}}
 {\endempheq}

\begin{document}

\section{Integrals}

Some text just to show alignment with the left margin
that should fill a line and go to the next one
\begin{boxedalign}
\textup{I.}\quad  & \int_a^b k \diff x = k(b - a) \\
\textup{II.}\quad & \int_a^b k \cdot f(x) \diff x = k \cdot \int_a^b f(x) \diff x
\end{boxedalign}

\end{document}