This is the last round of questions, I promise.

(1) Identify the space of all continuous linear functionals on the space .

(2) ,

Is Y closed vector space in X? What is the complement of Y?

(3) Prove that the series

converge for every vector

if and only if .

These are the last ones I don't know what to do with, and if anyone has the time and is willing to help, I would be really grateful.