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Homework Help: Basic set theory / mathematical notation

  1. Jul 15, 2009 #1
    I'm supposed to write the following intervals as sets in descriptive form:

    a. (t, infinity), t a fixed real number

    b. (0, 1/n), n a fixed natural number


    I think it is:
    a. (t, infinity) = {x: t < x < infinity}
    b. (0,1/n) = {x: 0 < x < 1/n}

    Is this correct?
    Also, how do you indicate that t is a fixed real number and n a fixed natural number?
  2. jcsd
  3. Jul 15, 2009 #2
    This seems fine. The only comment I will make is that I don't think you need the infinity in the "descriptive form". The extended real number system is defined so that {x: t < x} would suffice, iirc.
  4. Jul 19, 2009 #3
    I agree with snipez90's comment. Also, it would be good to be explicit about what x, t, and n are. You would notate this as [itex]x\in\mathbb{R}[/itex]. To say that t is a fixed real number, just say [itex]t\in\mathbb{R}[/itex], and to say that n is a fixed natural number, just say [itex]n\in\mathbb{N}[/itex].
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