Question

as,the set of real number is open?

Answer 1

yes the set of real is open because it doesn't have terminating value.

Answer 2

Answer:

By definition, a set A of real numbers is open when the following condition is met: ∀x∈A,∃ϵ>0 such that (x−ϵ,x+ϵ)⊂A, where (a,b) denotes the open interval {x∈R|a<x<b}.