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Homework Help: Help-How to Prove It, Sec.4.4, 18b

  1. Oct 19, 2011 #1
    1. The problem statement, all variables and given/known data
    The real problem is my professor makes anyone who asks a question in class or office hours feel like a total idiot. I

    Sec.4.4 Problem 18a) https://www.physicsforums.com/showthread.php?t=541479

    Could someone comment on whether it would be okay to use part a) in part b)?
    2. Relevant equations
    Above we proved, for all x element of A, x is an upper bound of B1 iff x is an upper bound of B2.
    Can we use this in part b)? Although b) is talking about a maximal element instead of an upper bound. I think the only difference is that maximal element is part of the subset.

    3. The attempt at a solution
    Contra positive. Assume B1 has a maximal element b1. This means that there does not exist an x є B1(b1Rx Λ b1 ≠ x). By part a), we know that b1 is also the maximal element of B2. Therefore, b1 є (B1 and B2). Therefore, B1 and B2 are not disjoint.
    Last edited: Oct 19, 2011
  2. jcsd
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