Hi the problem that I have is to show

where

is a rational number. (Also on the sum sign there is

on top and

on bottom.

I know what I need to do to start which is show

but my problem is I find it really hard to realise where the common factors are and what I should, if anything expand anywere. I would be really greatful if someone could post a step by step method on how they would do this explaing what has been extracted and what has been expanded. I know its seems alot but I would be really greatful. Thankyou!