Equations alignment Keynote

The following works correctly on Keynote versions 9.1 (High Sierra), 10.1 (Mojave), and 12.0 (Big Sur/Monterey):

\begin{aligned}

x^2 - 2x - 63 &= 0 \\
(x + 7)(x - 9) &= 0 \\
x &= -7,9

\end{aligned}

None of Pages, Numbers, or Keynote have a clue about LaTeX/MathML syntax without using the blahtex translator within the applications to convert the input syntax into an embedded MathML object. That blahtex translator is quite limited to what syntax that it will accept which is a dramatic departure from what a real TeX/LaTeX implementation (e.g. MacTeX 2022) permits.

Apple discussed the LaTeX/MathML equation capabilities/restrictions within these applications when the equation functionality was introduced in macOS Sierra:

About LaTeX and MathML support in Pages, Numbers, Keynote, and iBooks Author - Apple Support

I recommend that you obtain the blahtex PDF (linked in the above article) and keep that handy too.

There are sections in the Pages, Numbers, and Keynote User Guides about adding equations:

Format fractions automatically in Pages on Mac - Apple Support

Add mathematical equations in Numbers on Mac - Apple Support

Add mathematical equations in Keynote on Mac - Apple Support

This should work... (from the Insert menu, choose Equation, enter the following in the pop-up LaTeX editor):

\begin{align}

x^2-2x-63 &= 0\\

(x +7)(x-9) &=0\\

x& = 7,9

\end{align}

There is no animation involving the Keynote equation editor, so you will need alternative means to make equations appear in sequence…