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Some help on sets, please!

by hikki_pop
Tags: sets
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hikki_pop
#1
Jun15-04, 04:58 AM
P: 17
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)

thanks !!

sorry for the double post!! please delete this one!!!
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NeutronStar
#2
Jun17-04, 11:06 PM
P: 418
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}
HallsofIvy
#3
Jun20-04, 07:03 PM
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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".

NeutronStar
#4
Jun20-04, 08:04 PM
P: 418
Some help on sets, please!

Quote Quote by 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".
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.


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