# Homework Help: Intersection of an infinite set

1. May 29, 2010

### michonamona

Let $$G_{n}$$ = (-1/n,1/n) for all n in N

let $$G= \bigcap^{\inft}_{n=1}$$
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. May 29, 2010

### irycio

So, what's the question/problem?? The intersection is simply 0 (zero, a single number). Hence the intersection of an infinite number of open sets is not necessarily open, whereas the union is always open, as is the finite intersectiion of them. With the closed sets, it's the other way round :).