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Homework Help: Proving a Discrete math problem

  1. Feb 25, 2010 #1
    Another one of my homework asks is this true or false and prove it:

    For all sets A, B, and C if A U C is a subset of B U C then A is a subset of B

    Please help!
     
  2. jcsd
  3. Feb 25, 2010 #2

    ideasrule

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    Always try to come up with a counterexample. What happens if C is the set of all living things and A is the set of all humans?
     
  4. Feb 26, 2010 #3
    Consider
    [tex]A = \{ 1 \}[/tex]
    [tex]B = \{ 3 \}[/tex]
    [tex]C = \{ 1, 2 \}[/tex]
     
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