关于枚举开始时换行的快速问题

Question

首先，这是序言：

    \documentclass[a4paper,12pt]{report}
\usepackage{physics}
\usepackage{amsthm,amssymb,thmtools}
\usepackage{graphicx}
\usepackage{epstopdf}
\usepackage{caption}
\usepackage{subcaption}
\usepackage{enumerate}
\usepackage{framed}
\usepackage{mathtools}
\usepackage{empheq}
\usepackage{relsize}
\usepackage{nicefrac}

\newcommand*\widefbox[1]{\fbox{\hspace{1em}#1\hspace{1em}}}


\renewcommand{\thechapter}{\Roman{chapter}}
\newtheorem{theorem}{Theorem}
\renewcommand{\thetheorem}{\arabic{chapter}.\arabic{theorem}}
\renewcommand*{\arraystretch}{1.5}

\declaretheoremstyle[spaceabove = 3pt, spacebelow = 3pt, headpunct={:} ,postfoothook=\noindent\hspace{-\fontdimen2\font},postheadspace=\newline]{mydef}

\declaretheoremstyle[spaceabove = 3pt, spacebelow = 3pt, headpunct={:} ,postfoothook=\noindent\hspace{-\fontdimen2\font},headfont = \itshape,postheadspace=\newline]{mysol}

\declaretheoremstyle[spaceabove = 3pt, spacebelow = 3pt, headpunct={:} ,postfoothook=\noindent\hspace{-\fontdimen2\font}]{myrem}

\declaretheoremstyle[spaceabove = 3pt, spacebelow = 3pt,headpunct = {!}, postfoothook=\noindent\hspace{-\fontdimen2\font},headfont=\itshape]{mycare}

\declaretheoremstyle[spaceabove = 3pt, spacebelow = 3pt,headpunct = {:}, postfoothook=\noindent\hspace{-\fontdimen2\font},headfont=\itshape]{myint}

\declaretheorem[parent=chapter,name = Def,style = mydef]{definition}
\renewcommand{\thedefinition}{\arabic{chapter}.\arabic{definition}}

\declaretheorem[parent = chapter,style = mydef, name = Example]{example}
\renewcommand{\theexample}{\arabic{chapter}.\arabic{example}}

\renewcommand{\thefigure}{\arabic{figure}}

\declaretheorem[style=myrem,numbered=no]{remark}
\declaretheorem[style=mycare, numbered = no]{careful}
\declaretheorem[style=myint, numbered = no]{interpretation}
\declaretheorem[style=myrem, numbered=no]{visualization}
\declaretheorem[style=mysol,numbered = no]{solution}

以下是有问题的代码：

\begin{solution}
        \begin{enumerate}[(i)]
            \item $r = \sqrt{x^2+y^2} = \sqrt{9+3} = \sqrt{12}$
            \item We need $\varphi$ such that 
            \[(3,\sqrt{3}) = (r \cos \varphi, r \sin \varphi) = \sqrt{12}(\cos \varphi, \sin \varphi )  \]
        \end{enumerate}
    \end{solution}

输出如下：

我怎样才能使枚举中的第一个项位于下一行，并且两个索引正确排列。我担心我的代码中某个地方的拼写错误导致了这种情况，或者我没有正确理解如何声明新的定理样式并应用它们。正如您在“mysol”样式中看到的，我已经写了，postheadspace=\newline尽管事实并非如此。

谢谢您的帮助。

Answer 1

从一个空项目开始。

\begin{solution}
        \begin{enumerate}[(i)]
            \item[] % <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
            \item $r = \sqrt{x^2+y^2} = \sqrt{9+3} = \sqrt{12}$
            \item We need $\varphi$ such that 
            \[(3,\sqrt{3}) = (r \cos \varphi, r \sin \varphi) = \sqrt{12}(\cos \varphi, \sin \varphi )  \]
        \end{enumerate}
\end{solution}