# Some help on sets, please!

1. Jun 15, 2004

### hikki_pop

can anyone tell me the answer to this??

if
U (universal set) = {1,2,3,4,5,6,7,8,9,10,11,12,13,14}
C (just a simple subset of the universal set U)= {1,2,3,4,5}

then what would be the answer if:

C U U' ????? (subset C union universal set complement)

:yuck: thanks !!

sorry for the double post!! please delete this one!!!

2. Jun 17, 2004

### NeutronStar

Don't you need to also include your universe of discourse?

If your universe of discourse is the natural numbers then,...

C U U' would be {1,2,3,4,5} U {15,16,17,...}

If your universe of discourse is the integers then,...

C U U' would be {... -3,-2,-1,0} U {1,2,3,4,5} U {15,16,17,...}

For other universes of discourse it could get ugly. :surprise:

Edited to add the following possibility,...

If your universe of discourse is U then U' is the empty set so,...

C U U' would be just be {1,2,3,4,5}

Last edited: Jun 17, 2004
3. Jun 20, 2004

### HallsofIvy

Neutron star: the original post said "U (universal set) = 1,2,3,4,5,6,7,8,9,10,11,12,13,14}.

That is the "unverse of discourse".

4. Jun 20, 2004

### NeutronStar

That's normally what I would assume too, but I've found that different people use different notations including college professors and textbook authors. I've seen the term universal set used to refer to a specific set while the author (or professor) continues to treat the problem as though the universe of discourse is still the natural numbers.

I would agree that they are technically incorrect in doing this. But they seem to do it quite often just the same. I've actually confronted a college professor about this once and all I got in return was a lecture on the difference between a universal set and the universe of discourse.

Don't look at me. I'm with you! As far as I'm concerned professors and authors who think there is a difference are wrong. But since its an imperfect universe (no pun intended) I like to cover all my bases.