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Mathmatical proofs help please

  1. Dec 4, 2011 #1
    Mathmatical proofs help please!!

    1. Must two uncountable sets have the same cardinality?
    a countable union of countable sets is countable.
    Is a finite set necessarily countable?
    If the union of A and B is infinite, then A or B must be inifinte



    2. Just use definitions of Uncountable, Countable, finite, and infinite, and cardinality to do these proofs.


    3. I know what the answers are just by thinking but I cannot prove the answers please help or I will fail
     
  2. jcsd
  3. Dec 4, 2011 #2

    Dick

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    Re: Mathmatical proofs help please!!

    Well, state the definitions, then state what you are thinking and try to use the definitions to prove what you thinking. You have to give us something to go on.
     
  4. Dec 4, 2011 #3

    hunt_mat

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    Re: Mathmatical proofs help please!!

    The cardinality of a finite set is just the number of elements of that set.
     
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