# Problem with proving

• Oct 13th 2011, 12:11 PM
Scorpy6
Problem with proving
I need to show that A is a subset of B if and only if A union B is equal to B. Can somebody help me with this? Thanks :)
• Oct 13th 2011, 12:59 PM
CaptainBlack
Re: Problem with proving
Quote:

Originally Posted by Scorpy6
I need to show that A is a subset of B if and only if A union B is equal to B. Can somebody help me with this? Thanks :)

You need to show two things:

1. If $A \subset B$ then $A\cup B=B$

2. If $A\cup B$ then $A \subset B$

Now what have you tried and what problems are you having?

CB