Interesting...

well, you had the right idea at first:

let

Thus,

For this equation to be true,

Note that there is no given restriction on x. So we can generalize this and say that this equation is true when

the notation means that n is an element of the integer set (this lets us know that n can be ...-3, -2, -1, 0, 1, 2, 3,...).

I hope this makes sense!

--Chris