It is difficult. If we do go down the rabbit hole of designing a non-spatial transcription of the printed horizontal curly brace, then I suspect we must make it very clear what the printed braces are "embracing." That would be "x-squared equals thirty-six" and "x equals six or x equals minus six" In addition, it is probably not best practice to insert an opening curly brace in braille when only the closing curly brace is shown in print.
Thus, I think the following is what we would have to do:
;;<X9#B "7 #CF>.5<;',HYPO!SIS_>1 !N
;<X "7 #F OR ;X "7 "-#F>.5<;',3CLU.N_>
where braille grouping indicators enclose the "embraced" material and a directly below indicator precedes the "pointed to" material, which is enclosed with an opening braille grouping indicator and a closing curly brace.
Whew. I prefer the spatial approach. What do you think?
Corrected versions of all my examples are attached.