Given a power series of the form
$$f(z)=\sum_{n=0}^\infty a_nz^n$$ with $z\in\mathbb{C}$ and radius of convergence $R$, then itss derivatives is $$f’(z)=\sum_{n=1}^\infty n\,a_nz^{n-1}$$ with radius of convergence $R$.
Now, some texts define the derivative as $$f’(z)=\sum_{n=0}^\infty n\,a_nz^{n-1}$$ So my questions is, why do some texts use one and not the other? Which is the preferred use?
Basicaly it is same thing.If we start in last series with $n=0$ we would get first term $0$.That means we can start from $n=1$