Hello thereddevilsYour thoughts are correct, but you're not sure how to fit them together, are you? Look at the denominator like this. First, note that:
, or
whatever may stand for.
So if
In the same way, if , so:
... and so on. So the denominator becomes:
And we now note that is an infinite GP, with first term , common ratio , and with a sum to infinity of .
In the same way, the numerator is
And
So the original expression simply becomes
Grandad