如何在rmarkdown中正确对齐数学公式？

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$$
\begin{align*}
x &= y + z \\
a &= b + c
\end{align*}
$$

\\[
\begin{align*}
x &= y + z \\
a &= b + c
\end{align*}
\\]

$$
\begin{align*}
x &= y + z \\
a &= b + c
\end{align*}
$$

\\[
\begin{align*}
x &= y + z \\
a &= b + c
\end{align*}
\\]

$$
\begin{split}
x &= y + z \\
&= a + b + c \\
&= d + e
\end{split}
$$

\\[
\begin{split}
x &= y + z \\
&= a + b + c \\
&= d + e
\end{split}
\\]