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Proving a subset

  • #1

Homework Statement


The problem I have been given is to prove (A - B) U C is than less or equal to (A U B U C) - (A n B)



The Attempt at a Solution


I've tried starting off with just (A-B) U C. Then I would say how x ε c or x ε (A - B). Also if x ε a, then x ε c and x is not in b. If x ε c, since c is a subset of (A U B U C) , x ε (A U B U C). I don't know if this is right or where to go from here.
 

Answers and Replies

  • #2
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Homework Statement


The problem I have been given is to prove (A - B) U C is than less or equal to (A U B U C) - (A n B)
This is a statement about sets, so the relationship is [itex]\subseteq[/itex], not ≤.

The Attempt at a Solution


I've tried starting off with just (A-B) U C. Then I would say how x ε c or x ε (A - B). Also if x ε a, then x ε c and x is not in b.
Try to be more careful with the names of the sets, which are A, B, and C, not a, b, and c.
If x ε c, since c is a subset of (A U B U C) , x ε (A U B U C). I don't know if this is right or where to go from here.
 
  • #3
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0
i'd say that u can use:

AUBUC= lAl + lBl + lCl - lBnCl - lAnBl - lAnCl+lAnBnCl

but i'm not 100% positive just trying to give some help :)
 
  • #4
My professor said we can also try to prove or find a counterexample to this statement. Let A, B and C be sets. Then (A-B) U C = (A U B U C) - (A n B). I'm not really sure what she means by counterexample.
 
  • #5
HallsofIvy
Science Advisor
Homework Helper
41,806
932
i'd say that u can use:

AUBUC= lAl + lBl + lCl - lBnCl - lAnBl - lAnCl+lAnBnCl

but i'm not 100% positive just trying to give some help :)
Not only does that not help, it makes no sense. The left side is a set, the right side is a number.

Even if you meant |AUBUC| that is irrelevant to the problem. Showing that two sets have the same size does not prove they are the same set.
 

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