Newtheoremstyle head aligned with top of tabularx

Question

Here's an example :

\documentclass[12pt]{report}
\usepackage{amsmath, amssymb, amsthm}

\usepackage{tikz}
\usetikzlibrary{shadows}
\newcommand*\squared[1]{\tikz[baseline=(char.base)]{\node[shape=rectangle, draw, inner color = white, drop shadow = {opaque, black}, inner sep=3pt, text justified] (char) {#1};}}

\newtheoremstyle{exercise}
  {\topsep}
  {\topsep}
  {\hangindent=2em}
  {}
  {}
  {}
  {.8em}
  {\squared{\thmnumber{#2}}}

\theoremstyle{exercise}
\newtheorem{exercise}{}

\renewcommand{\arraystretch}{1.75}
\usepackage{tabularx}

\begin{document}

\begin{exercise}
    \begin{tabularx}{\textwidth}{r @{\hskip .4em} X}
        a) & This is a test. \\
        b) & This is a long test. \\
        c) & This is a very long test.
    \end{tabularx}
\end{exercise}

\end{document}

What I want is the number of the exercise to be aligned with the top of the tabularx (question a)) instead of being aligned with the middle of the tabularx.

Answer 1

Use t (top alignment) for the optional argument of tabularx:

\documentclass[12pt]{report}
\usepackage{amsmath, amssymb, amsthm}

\usepackage{tikz}
\usetikzlibrary{shadows}
\newcommand*\squared[1]{\tikz[baseline=(char.base)]{\node[shape=rectangle, draw, inner color = white, drop shadow = {opaque, black}, inner sep=3pt, text justified] (char) {#1};}}

\newtheoremstyle{exercise}
  {\topsep}
  {\topsep}
  {\hangindent=2em}
  {}
  {}
  {}
  {.8em}
  {\squared{\thmnumber{#2}}}

\theoremstyle{exercise}
\newtheorem{exercise}{}

\renewcommand{\arraystretch}{1.75}
\usepackage{tabularx}

\begin{document}

\begin{exercise}
    \begin{tabularx}{\textwidth}[t]{r @{\hskip .4em} X}
        a) & This is a test. \\
        b) & This is a long test. \\
        c) & This is a very long test.
    \end{tabularx}
\end{exercise}

\end{document}

Not related to the question, but to prevent an overfull \hbox you'll need to reduce the width for the tabularx.