i) Using the binomial theorem you have
Equate the co-efficients of
on both sides using the above for
.
On the LHS we have
and on the RHS we want the co-efficients of
since we are dividing by
. The second binomial clearly does not have a co-efficient of
so we need only to find the required co-efficient of the first binomial, which is
.
ii) from i) set
This gives
Subtract 1 and note that
for all
.
This gives
Rewriting in sigma notation, we get:
Rewrite the binomial on the LHS:
Multiply both sides by
:
And rewrite the LHS: