I wasn't sure where to put this, but here goes.

is a formula we have been given.

We have been told that the denominator is a factor when x is prime and we're expected to prove/show that to be the truth.

It works experimentally (substituting numbers) but I can't actually find a proper proof.

Best I could come up with is:

Let it equal

so that therefore b is a factor of a (a=by, y is an integer)

and

That leads me to subsitute them back and get:

which simplifies to give y, which is an integer.

Any proper proofs?