How to determine if for e.g. (3,0) is a closure point of a set C
where C=A ∩ B
Where A=1≤x^2+y^2≤9
B=IxI>1
How would I start something like this?
A point, P, is a closure point of set S (is in the closure of S) if and only if every open neighborhood of P contains a point of X. Here, (3, 0) is in set B and $3^2+ 0^2= 9$ so, for any $\epsilon> 0$, $(3- \epsilon, 0)$ is in C.