I’m stuck on something in generating functionology. The first problem asks: Find the ordinary power series generating functions of the sequence in simple closed form for the sequence $a_n = n$. The sequence is defined as $n ≥ 0$.
I figured out how to get to $A(x) = x/((1-x)^2)$. That’s not an issue.
However, the book lists the answer as $(xD)(1/(1-x)) = x/((1-x)^2)$
Where did the D come from? How can I get my answer in terms of D?