Math Is Fun Forum

hopless guy

Guest

help plz

Hey everyone, Im taking a course in Discrete math and am having a hard time with some of these topics.  For instance,  Im given

[ B' ∪ (B' - A) ] = B

Im asked to prove this by set identities.  Im lost as to what direction to take?  Can someone lend a helping hand?

Thanks alot in advance!

soroban

Member

Registered: 2007-03-09

Posts: 452

Re: help plz

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hopless guy

Guest

Re: help plz

sorry . i didn't know how to type it , so i just copy paste parts from different places ..  i'll re-write it informaly in sentences:

[ complement of (B) U ( complement of (B) - A ) ]complement

notice that there is a (c) over the outer braces ..

thank you so much for your time and effort ..

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actuly there is another one that i found out that we have to hand it to our TA , which is :

( A - B ) - ( B - C ) = A - B

.................

thanx in advance

Ricky

Moderator

Registered: 2005-12-04

Posts: 3,791

Re: help plz

Since B' - A is contained in B', you can easily simplify the inside to just one term.  Try to take it from there.

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"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

hopless guy

Guest

Re: help plz

sorry man , for the first one , i couldn't get it at all ,, i tried all the laws , but i was getting somewhere else , and sometimes i end up by going to the first step again ,
if you can kindly help me with the first one i'll appriciate it ,, P.S: the whole set is equal to B .. so we have to prove that it's equal to B

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the second one looks easier , with some hints i might be able to do it ..

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i appriciate your time

Ricky

Moderator

Registered: 2005-12-04

Posts: 3,791

Re: help plz

Do you see that

?

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"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."