Rectangle question and closure of the interior?

[Buri]

The question says:

Show that if Q = [a1,b1]x...x[an,bn] is a rectangle, the Q equals the closure of Int Q.

The definition of closure that I have is Cl(A) = int(A) U bd(A). So I'd like to show that Cl(int(Q)) = int(int(Q)) U bd(int(Q)).

But this just seems to be obvious to me which just makes it hard to prove - I just don't know what to write. Any hints/ideas on how to prove this rigorously?

EDIT!

I guess I'd have to show something like:

Int(AxB) = Int(A)xInt(B)

And then I guess, I'd make a claim that bd(int(Q)) = {a1,b1,...,an,bn} and prove this by showing that no other boundary points exist?

Questions like this I always find hard.

 

[VeeEight]

You are being asked to show that Q = Cl (IntQ)
You know how to define Int and Bd, so write out the definitions explicitly (in set theory notation) to show that they coincide.