You can always do a multi-line equation:
$$
$$
\begin{align*}
ax^2+bx+c&=0 \\
x&=\frac{-b\pm\sqrt{b^2-4ac}}{2a}
\end{align*}
$$
The $$ tells Obsidian that this is a multi-line equation. The \\ basically just represents a newline. Since it’s quite helpful, the \begin{align*} and \end{align*} will align everything containing a &, like &=, which will align the equal signs.
Hope this helps.