# Math Help - Set Theory Help.

1. ## Set Theory Help.

Ok guys, for any 2 non-empty sets X and Y drawn from the same univserse, U, let Z be defined
$Z = (A \cap ¬B) \cup (¬A \cap B)$

Therefore, $Z = A \Delta B$

I need to prove Z could equal Ø.
Also, Z can equal U.

Thanks for any help.

2. Originally Posted by Kostapoulous
Ok guys, for any 2 non-empty sets X and Y drawn from the same univserse, U, let Z be defined
$Z = (A \cap ¬B) \cup (¬A \cap B)$
Therefore, $Z = A \Delta B$
I need to prove Z could equal Ø.
Also, Z can equal U.
What if $A=B~?$.

3. $A\vartriangle B=\emptyset$ iff $A = B$.

$A\vartriangle B=U$ iff $A\cup B = U$ and $A\cap B=\emptyset$.

4. Originally Posted by Plato
What if $A=B~?$.
I don't quite follow what you mean, I was under the assumption that A could not equal B. I am quite confused.

5. Originally Posted by Kostapoulous
I don't quite follow what you mean, I was under the assumption that A could not equal B. I am quite confused.
If both are non-empty and $A\ne B$ then $A\Delta B\ne\emptyset.$

If $A\cap B=\emptyset$ then $A\Delta B=A\cup B$

6. Originally Posted by Plato
If both are non-empty and $A\ne B$ then $A\Delta B\ne\emptyset.$

If $A\cap B=\emptyset$ then $A\Delta B=A\cup B$
But if Z = $A\Delta B$ , i.e. the symmetrical difference, which is what is in set A but not B, and what is in set B but not A, how can it ever equal Ø if they are non-empty? Would they not always have some elements in the sets?

7. Originally Posted by Kostapoulous
But if Z = $A\Delta B$ , i.e. the symmetrical difference, which is what is in set A but not B, and what is in set B but not A, how can it ever equal Ø if they are non-empty? Would they not always have some elements in the sets?
$A\Delta B=\emptyset{\text{ if and only if }A=B.$

$A\Delta B\ne\emptyset{\text{ if and only if }A
\ne B.$

8. Originally Posted by Plato
$A\Delta B=\emptyset{\text{ if and only if }A=B.$

$A\Delta B\ne\emptyset{\text{ if and only if }A
\ne B.$
Yes! It's finally clicked in my head! I feel like such an idiot now for not picking this up earlier!