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Homework Help: Demorgan's law

  1. Feb 1, 2010 #1
    1. The problem statement, all variables and given/known data
    (A'B')'=A'+B' is a representation of DeMorgan's Law. True or false?


    3. The attempt at a solution
    Is this saying that not A and not B is equal to A nor B?? i'm confused because each individual letter has its own notation rather than AB together. idk if that made sense...
     
  2. jcsd
  3. Feb 1, 2010 #2

    Mark44

    Staff: Mentor

    This is saying - not(not(A) AND not(B)) = not(A) OR not(B).

    I don't understand what you're saying here "each individual letter has its own notation rather than AB together." There is no AB "together" as its own symbol. AB means A AND B.
     
  4. Feb 1, 2010 #3
    ohhh. ok. that makes more sense. but is it possible for not(not(A) AND not(B)) to become an OR problem?
     
  5. Feb 1, 2010 #4

    Mark44

    Staff: Mentor

    I don't know - maybe. That's what your problem is all about. There are two forms of DeMorgan's Law:

    ~(A AND B) = ~A OR ~B
    ~(A OR B) = ~A AND ~B
    The tilde - ~ - is commonly used for negation (i.e., "not").

    In your problem, work with one of the sides and see if you can make it look like the other.
     
  6. Feb 1, 2010 #5
    my thoughts are that this would be false because it would have to be
    ~(~A and ~B) = ~(~A or ~B)
     
  7. Feb 1, 2010 #6

    Mark44

    Staff: Mentor

    No, ~(~A and ~B) = ~(~A) or ~(~B), right?

    What is ~(~A)?
     
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