Consider $\mathbb C^n$ as a Banach algebra over $\mathbb C$. Is it semisimple?
A Banach algebra is semisimple if the intersection of all maximal ideals of it is ${0}$.
I can't figure out what are the maximal ideals of $\mathbb C^n$. How do I solve it?
What about putting $I_k:=\{x\in\mathbb{C}^n\mid x_k=0\}$?
They are surely ideals, they are maximal since their dimension is $n-1$, and their intersection is zero.