I need some help showing that if S and T are subrings of R, then the union of S and T is a subring of R. Any ideas how to start?

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- February 9th 2009, 07:03 PMEagle3Unions of subrings
I need some help showing that if S and T are subrings of R, then the union of S and T is a subring of R. Any ideas how to start?

- February 9th 2009, 08:18 PMThePerfectHacker
- February 9th 2009, 09:09 PMEagle3Union of subrings
Are you saying that the same argument holds for S U T. If so, isn't there a possibility that a+b could be in R, but not in S U T?

- February 9th 2009, 09:33 PMThePerfectHacker
- February 9th 2009, 09:35 PMEagle3Union of subrings
That is what I thought. I just could find a way to prove that it was true and logically I could see where it might not be true.

Thanks