Insert numbered equation on Pages using LaTeX

You don't, because you are not dealing with LaTeX, but a binary (blahtex) converter that sits behind the Pages equation editor, and it transforms limited LaTeX syntax into MathML that is embedded into the Pages document. It excludes equation numbering, and most of the power of LaTeX.

More on Page's equation editor support for LaTeX syntax, and a direct link to the blahtex translator PDF guide.

You could wing this with a borderless, single-row, two column table with the equation inserted into the first cell, and the manually inserted equation number in the right column. Feasible, but not much fun.