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\title{Differential Equations}
\author{Jose M. Serra Jr.}
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\textbf{Series Solutions of Linear Equations}
\textbf{Review of Power Series}
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l.83
我有个问题，我的新命令有什么问题？我读了网站上的一篇文章，他们做了类似的事情，所以我试着做了一个自己的命令，但没有用。
答案1
考试
\ifx \relax[
测试两个标记\relax，[并且由于它们不相等，所以它始终为假。
你可能打算
\ifx\relax#1\relax
更好的写法是
\if\relax\detokenize{#1}\relax
测试是否#1为空（如果为空，则\relax比较两个标记，结果相等）
但这将允许如下语法
\formula{a=b}{}{}
宏\formula总是有三个参数，你只是测试参数是否为空（{}）。所以在
\formula{f(x)}
\end
这三个参数分别是f(x)、\par（来自空白行）和\end（用于\end{document}）。
除了这些问题之外，您\par之前一直在强制解决\begin{equation}，但这总是会导致间距不佳。
最好使用多行显示，这样允许任意数量的行无需测试。
\documentclass{article}
\usepackage{amsmath}
\begin{document}
one
\begin{equation}
eq:a=b
\end{equation}
two
\begin{gather}
a=b\\
c=5
\end{gather}
lots
\begin{gather}
a=bb\\x=y\\f=u\\77=77\\aaa=bbb
\end{gather}
\end{document}