I try to format my math like this in MathJax:
How can I do long division of polynomials in MathJax?
Old post, but I couldn't find an answer elsewhere, so here's how I solved this issue with two side-by-side arrays. Couldn't figure out how to make the lines shorter as I could in LaTex, but this was good enough for me:
<span class="math display">\[\begin{array}{r}
\\
x^2 - 3) \\
\phantom{.} \\
\phantom{.} \\
\phantom{.} \\
\phantom{.} \\
\phantom{.} \\
\phantom{.} \\
\phantom{.} \\
\phantom{.} \\
\phantom{.} \\
\end{array}
\begin{array}{rrrrrr}
& & x^3 & -2x^2 & +4x & -6 \\ \hline
x^5 & -2x^4 & + x^3 & &-8x & +18 \\
-x^5 & &+3x^3 \\ \hline
& -2x^4 & +4x^3 \\
& 2x^4 & &-6x^2 \\ \hline
& & 4x^3 & -6x^2 & -8x \\
& & -4x^3 & &+12x \\ \hline \\
& & &-6x^2 & +4x & +18 \\
& & & 6x^2 & & -18 \\ \hline
& & & & 4x
\end{array}\]</span>