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Math Help - proof valid by modus tollens??

  1. #1
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    proof valid by modus tollens??

    p--->q or r
    not q ^not r
    ___________
    therefore not p
    Is this valid by Modus tollens???? or is it invalid because you can not go in reverse order??? Thank you to anyone who can untangle my thinking on this one.
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  2. #2
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    Quote Originally Posted by frostking2 View Post
    p--->q or r
    not q ^not r
    ___________
    therefore not p
    Is this valid by Modus tollens???
    It is valid by Modus tollens.
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