1. Let X be R be a finite set and define f : R [tex]\rightarrow[/tex] R by f(x) = 1 if x [tex]\in[/tex] X and f(x) = 0 otherwise. At which points c in R is f continuous? Give proofs. 3. I don't know how to start this, do you think it is ok to assume that X represents an interval of R? If not how can you possibly deduce the points continuity?