If , we define the boundary of A by the equation(a) Show that Ini A and Bd A are disjoint,...

If , we define the boundary of A by the equation

(a) Show that Ini A and Bd A are disjoint, and .

(b) Show that Bd  is both open and closed.

(c) Show that U is open

(d) If U is open, is it true that  Justify your answer.