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Math Help - Use of Quantifiers

  1. #1
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    Use of Quantifiers

    Another example from my textbook that I can't quite figure out. Let p(x), q(x) denote the following open statements.

    p(x): x ≤ 3
    q(x): x + 1 is odd

    If the universe consists of all integers, what are the truth values of the following statements?

    a) q(1)
    b) p(3)
    c) p(7) v q(7)
    d) p(3) ^ q(4)
    e) (p(-4) v q(-3))
    f) p(-4) ^ q(-3)
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  2. #2
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    Re: Use of Quantifiers

    Quote Originally Posted by rhymin View Post
    Another example from my textbook that I can't quite figure out. Let p(x), q(x) denote the following open statements.
    p(x): x ≤ 3
    q(x): x + 1 is odd

    If the universe consists of all integers, what are the truth values of the following statements?
    a) q(1)
    b) p(3)
    c) p(7) v q(7)
    d) p(3) ^ q(4)
    e) (p(-4) v q(-3))
    f) p(-4) ^ q(-3)
    We do not do your homework for you.

    But I will help you.
    For c) 7\not\le 3 and 7+1\text{ is not odd}. So is c) true or false? WHY?
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  3. #3
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    Re: Use of Quantifiers

    This isn't homework. I am taking a math class in about a month and am studying a textbook that I believe will help. Am I posting in the right forum? The questions I am posting are ones that didn't have great examples and are confusing to me.
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    Re: Use of Quantifiers

    c) 7 is not less than or equal to 3 and 8 is not odd. so since both are false, it is false.

    What happens if one is true and one is false?
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    Re: Use of Quantifiers

    Quote Originally Posted by rhymin View Post
    c) 7 is not less than or equal to 3 and 8 is not odd. so since both are false, it is false.
    What happens if one is true and one is false?
    That is not the question! It has nothing to do with it.

    c) Asks if [p(7) \vee q(7) is a true statement? When is an or, disjunction, true?
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  6. #6
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    Re: Use of Quantifiers

    It is not a true statement. I'm just not sure what "truth values" means.
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    Re: Use of Quantifiers

    Quote Originally Posted by rhymin View Post
    I'm just not sure what "truth values" means.
    There are only two truth values: TRUE (T) or FALSE (F).

    In this question p(0) has a truth value of T and p(4) has truth value of F.
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  8. #8
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    Re: Use of Quantifiers

    Okay I learned a bit more about these symbols.
    Are these right?

    b) p(3): not 3 ≤ 3 = False

    c) p(7) v q(7): 7 ≤ 3 or 7 + 1 is odd...both are false, so it is False

    d) p(3) ^ q(4): 3 ≤ 3 and 4 + 1 is odd...one is true, one is false, so it is False (since both must be true)

    e) (p(-4) v q(-3)): (-4 ≤ 3 or -3 + 1 is odd)...one is false, one is true, so it is True

    f) p(-4) ^ q(-3): -4 ≤ 3 and -3 + 1 is odd...one is false, one is true, so it is False
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  9. #9
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    Re: Use of Quantifiers

    Quote Originally Posted by rhymin View Post
    Okay I learned a bit more about these symbols.
    Are these right?

    b) p(3): not 3 ≤ 3 = False

    c) p(7) v q(7): 7 ≤ 3 or 7 + 1 is odd...both are false, so it is False

    d) p(3) ^ q(4): 3 ≤ 3 and 4 + 1 is odd...one is true, one is false, so it is False (since both must be true)

    e) (p(-4) v q(-3)): (-4 ≤ 3 or -3 + 1 is odd)...one is false, one is true, so it is True

    f) p(-4) ^ q(-3): -4 ≤ 3 and -3 + 1 is odd...one is false, one is true, so it is False
    d) is true because both are true.
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  10. #10
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    Re: Use of Quantifiers

    Wow, I'm not sure how I missed that lol. What about (e)? Is that one also True? Doesn't just 1 have to be true with the "v" (or) symbol for it to be true? Or am I off there?
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  11. #11
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    Re: Use of Quantifiers

    e) (p(-4) v q(-3)): (-4 ≤ 3 or -3 + 1 is odd)...one is false, one is true, so it is True
    You are missing the "not" at the start aren't you?
    " -4\le 3" is true, "-3+ 1 is odd" is false so the statement "one of p(-4) OR q(3) is true" is true which means that "NOT....." is false.
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  12. #12
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    Re: Use of Quantifiers

    Ohhh i see now. Thank you so much for that. What I was doing was saying the first is true and second is false, and then just switching them. But I see that you are supposed to conclude that the entire statement is either true or false, and then use the negation symbol.
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  13. #13
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    Re: Use of quantifiers

    NB: Statements (e) and (f) are logically equivalent: they are either both true or both false.
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