elementary number theory - Divisibility and the gcd

Let $a,b$ be integers with $a|b$ (a divides b) and let $a>0$. Show that $(a,b)=a$. I know this is very basic, and that I'm complicating it unnecessarily, but for some reason I seem to be stuck...

Any help please?

Thanks.

Edit:
$(a,b)$ means greatest common divisor of $a$ and $b$

Answer

Well, recall the definition of $(a,b)$: it's the integer that divides both $a$ and $b$, and furthermore is the biggest integer that does so.

So how about asking:

1. Does $a$ divide $a$ and $b$?


2. Is $a$ the biggest integer that does so?

Hopefully this makes it obvious.