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Math Help - proof by contraposition help

  1. #1
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    proof by contraposition help

    1. m is an integer. Prove by contraposition that if 5m + 4 is odd then m is odd
    2. suppose m is even, than

      m = 2n for some n in N

      so

      5(2n) +4 = 20n+4

      factor out 2 = 2(10n+2)

      which is even, have i proved this ? ]
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  2. #2
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    Re: proof by contraposition help

    Quote Originally Posted by Tweety View Post
    1. m is an integer. Prove by contraposition that if 5m + 4 is odd then m is odd
    2. suppose m is even, than

      m = 2n for some n in N

      so

      5(2n) +4 = 20n+4

      factor out 2 = 2(10n+2)

      which is even, have i proved this ? ]
    Yep. A=5m+4 is odd, B=m is odd, show ~B --> ~A which is what you did.
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