I´m having a hard time getting through these sum understanding exercises

This one in particular, If you have some idéa, I value some explaining more then solution so please no: Hey stupid, what the hell, just to the "inversetriangular root extraction recursive absolute value differential" method and you got it!! That just makes me even more confused when I dont understand what I am suppose to do.

The troublesome exercise is:

Look at the series of:

of

where

with

and Show that is a geometric series with Constant when =:

where

Here is my current confused work:

Well I figured lets try some different values on and se what happens, then clearly goes towards 3. Well that info could be usefull (I suppose a little sometimes). graph looks like graph shiften left 3 units and up 5 units.

Now lets get on one side and everything else on another and se what happens:

so:

1)

2)

3)

4)

5)

6)

if I set I get

but if I set into the formula it goes

=

And here I am not sure what I´ve done or what I shouldn´t have done...