x-¹
Where I come from, that's read as "x to the [power of] minus one". "x minus one" is, well, x - 1. Not the same thing at all.
(I admit, my chances of deciphering what you meant might not have been all that high even if you'd used the correct phrasing, but without it, the chance was zero.)
We may also be separated by a common llanguage—"lecturer" isn't a word that's much used in Canada. I've only encountered it as a Briticism.