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Math Help - question about validating an argument

  1. #1
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    question about validating an argument

    I am trying to detrmine whether this argument is valid or not:

    p → q
    ∼p

    ∴∼q

    I did not see this as modus ponens or modus tollens.

    But I described it as:

    p: I walk my dog
    q: he is happy

    p → q: if I walk my dog he is happy
    ~p: I did not walk my dog

    therefore

    ~q: he is not happy

    This is not valid according to the table there could be two different outcomes.

    is this correct?

    p|q|p → q| ~p|~q

    T|T|T |F |F
    T|F|F |F |T
    F|T|T |T |F
    F|F|T |T |T

    Is this correct?

    If now please explian how to prove (valid) or (invalid)?
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  2. #2
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    Let P:x>3 and Q:x-1>0.
    If x=2 you have \neg P do you have \neg Q?
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  3. #3
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    yes
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  4. #4
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    Quote Originally Posted by robasc View Post
    yes
    Yes what?

    You have \neg(2-1>0)?
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  5. #5
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    yes it is false
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  6. #6
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    Well then the argument is not valid.
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  7. #7
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    this is known as a fallacy, denying the antecedent correct?
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  8. #8
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    Yes. What is the point of all this?
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  9. #9
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    I am double checking myself to make sure I am understanding the material correctly?
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