1. ## 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

2. ## Re: Problem with proving

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