If $f$, $g$ $\in End(V)$ are commuting, then it's:
$(f+g)^n=\sum_{k=0}^{n}{\begin{pmatrix} n\\k \end{pmatrix}}f^{n-k}\circ g^k$ for all $n \in \mathbb{N_0}$
I tried to compute it with the binomial theorem but i didn't get the result. How can it be done?