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Homework Help: Truth tables - I don't get it

  1. Feb 10, 2010 #1
    1. Demonstrate by means of truth tables the validity of the following identities.

    a) DeMorgan's theorem for two variables

    X'Y' = X' + Y'

    ' is the bars that are above the letters.




    Can someone explain this to me? I mean the truth table is just gonna look like this: X'Y' X' Y'
    I just need to know where and 0's and 1's go and why. Seems so easy, but I haven't been able to understand it.
     
  2. jcsd
  3. Feb 10, 2010 #2

    berkeman

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    Staff: Mentor

    Your table will have 4 coulmns. Fist is X, second is Y, third is X'Y' and forth is X' + Y'.

    Well, except that I think you forgot something in your statement of DeMorgan's Law.

    EDIT -- it's just a typo in how you wrote it out...
     
  4. Feb 10, 2010 #3

    Thanks. I just thought it was 3. How do I find out about the 0's and 1's ? I know DeMorgan's but don't know how to apply it to this one.
     
  5. Feb 10, 2010 #4

    berkeman

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    Staff: Mentor

    (hint -- check out the wikipedia.org page on DeMorgan's Law....)
     
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