I have a set i.e the diagonal of the unit square. How to show that A is closed??
By definition a set is closed if it's complement is open, so I need to show that is an open set. What will be in this case?
thank you for the help. I have a question.
Just to clarify
is the radius of the open ball ? (from the formula I get in the denominator)
What about the end points of A? Don't we have to find open balls in the neighborhood of these two with the proper radius?