# Thread: set related question ... need confirmation if I am doing this correct :-)

1. ## set related question ... need confirmation if I am doing this correct :-)

I need some help with understanding this question as well:

==================================== A – B = {x|x A x B}
A = {a, b, e, f}
B = {b, d, g, f, a}

Match the following to the correct answers.
A – B = ?
B – A = ?

a. {a, b, f}
b. {a, b, e, f}
c. {d, g}
d. {e}
====================================

What I understand here is that x has elements in A and that those elements are not part of B.
So when we do A - B the correct answer is: c. {a, b, f}

and B - A would be: c. {d, g}
Is this correct?

Thanks,

2. ## Re: set related question ... need confirmation if I am doing this correct :-)

Originally Posted by iwan1981
A – B = {x|x A x B} A = {a, b, e, f} B = {b, d, g, f, a} Match the following to the correct answers. A – B = ? B – A = ?

$A-B=\{e\}$ and $B-A=\{d,g\}$

3. ## Re: set related question ... need confirmation if I am doing this correct :-)

Originally Posted by FernandoRevilla
$A-B=\{e\}$ and $B-A=\{d,g\}$
How did you get this answer ... and what was I doing wrong?

4. ## Re: set related question ... need confirmation if I am doing this correct :-)

Originally Posted by iwan1981
I need some help with understanding this question as well:

==================================== A – B = {x|x A x B}
A = {a, b, e, f}
B = {b, d, g, f, a}

Match the following to the correct answers.
A – B = ?
B – A = ?

a. {a, b, f}
b. {a, b, e, f}
c. {d, g}
d. {e}
====================================

What I understand here is that x has elements in A and that those elements are not part of B.

No. x is not a set. It represents a element in A-B. So your statement should be corrected as, "A-B includes all the elements in A which are not in B".

So when we do A - B the correct answer is: c. {a, b, f}

This is incorrect as a,b and f are in B.

and B - A would be: c. {d, g}

Is this correct?

Correct

Thanks,
.

5. ## Re: set related question ... need confirmation if I am doing this correct :-)

I understand now ... that's why the ∉ (elements not in) comes into play ... I should've seen that one :-)