By definition, an isolated point x of a set S is a point of S. Also, an interior point of a set S can be defined by the mean of the existence of a positive number r>0 such that : wherein D(x,r) is the disc of center x and radius r.
Example of a set whose boundary is not a subset of S:
The answer is B. The first number in the sequence is going to be 2 and the second is going to be 7. you can plug those numbers in the check your answer but I already did it lol. Hope this helps!!
