Interior, Closure and Boundary of sets

A little topology (I think) problem here:

For A:= [0,1) ∪ ([2,3] ∩ http://upload.wikimedia.org/wikipedi...d9cf5fa79f.png) ∪ {5} ⊂ R (real numbers) find the closure, boundary and interior of A

I know the definitions but I don't know how to actually calculate them

Re: Interior, Closure and Boundary of sets

To compute the closure, just notice that the closure of a finite union is the union of the closures.

For the interior, can the points of $\displaystyle \left[2,3\right]\cap \mathbb Q$ be in it? And what about $\displaystyle \left\{5\right\}$?

Re: Interior, Closure and Boundary of sets

Quote:

Originally Posted by

**fylth**

Do you know that $\displaystyle \overline{A\cup B}=\overline{A}\cup\overline{B}~?$

$\displaystyle \overline{[0,1)}=[0,1],~\overline{[2,3]\cap\mathbb{Q}}=[2,3],~\&~\overline{\{5\}}=\{5\}$

Re: Interior, Closure and Boundary of sets

The boundary is the closure toss (set difference) the set...

The interior is...