如何调整以下拆分方程以使其左对齐

Question

我想让 LHS 上的拆分方程左对齐。我的 2 个尝试如下所示，即选项 A 和选项 B。请参阅源代码了解详细信息。

\documentclass[10pt]{article}
\usepackage[a6paper,vmargin=15mm,hmargin=5mm]{geometry}
\usepackage{mathtools}

\begin{document}
\begin{enumerate}
    \item Hey baby!
    \item
    $\!
    \begin{aligned}[t]
    2-3x(x-1)\\
    {}-3(x-2y)(x+2y)
        &=  \!
                \begin{multlined}[t][4cm]
                    2 -3x^2 +3x\\
                    {}-3(x^2 +2xy -2xy -4y^2)
                \end{multlined}\\
        &=  \!
                \begin{multlined}[t][4cm]
                    2 -3x^2 +3x\\
                    {}-3(x^2 -4y^2)
                \end{multlined}\\
        &=  \!
                \begin{multlined}[t][4cm]
                    2 -3x^2 +3x\\
                    {}-3x^2 +12y^2
                \end{multlined}\\
        &= -6x^2 +3x +12y^2 +2
    \end{aligned}
    $
    \item
    $\!
    \begin{aligned}[t]
    \begin{multlined}[t][4cm]
    2-3x(x-1)\\
    {}-3(x-2y)(x+2y)
    \end{multlined}\\
        &=  \!
                \begin{multlined}[t][4cm]
                    2 -3x^2 +3x\\
                    {}-3(x^2 +2xy -2xy -4y^2)
                \end{multlined}\\
        &=  \!
                \begin{multlined}[t][4cm]
                    2 -3x^2 +3x\\
                    {}-3(x^2 -4y^2)
                \end{multlined}\\
        &=  \!
                \begin{multlined}[t][4cm]
                    2 -3x^2 +3x\\
                    {}-3x^2 +12y^2
                \end{multlined}\\
        &= -6x^2 +3x +12y^2 +2
    \end{aligned}
    $
\end{enumerate}
\end{document}

如何解决这个问题呢？

Answer 1

这将为您提供选项 b：

\documentclass[10pt]{article}
\usepackage[a6paper,vmargin=15mm,hmargin=5mm]{geometry}
\usepackage{mathtools}

\begin{document}
\begin{enumerate}
\setcounter{enumi}{2}
\item
$
  \begin{multlined}[t]
  2-3x(x-1)\\
    \begin{aligned}
    {}-3(x-2y)(x+2y)
    &=  \!
            \begin{multlined}[t][4cm]
                2 -3x^2 +3x\\
                {}-3(x^2 +2xy -2xy -4y^2)
            \end{multlined}\\
    &=  \!
            \begin{multlined}[t][4cm]
                2 -3x^2 +3x\\
                {}-3(x^2 -4y^2)
            \end{multlined}\\
    &=  \!
                \begin{multlined}[t][4cm]
                    2 -3x^2 +3x\\
                    {}-3x^2 +12y^2
                \end{multlined}\\
        &= -6x^2 +3x +12y^2 +2
    \end{aligned}
  \end{multlined}
$
\end{enumerate}

\end{document}