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Homework Help: Simple sup and inf questions

  1. Oct 11, 2013 #1
    find the sup and inf of the following sets:

    [tex] { x | x^2 - 5x + 6 < 0 } [/tex]

    I got the inf and sup to be 2 and 3 respectively

    [tex] { x^2 - 5x + 6 | x \in ℝ} [/tex]
    here I was rather confused what this is saying. I'm assuming it's taking about the graph x^2 - 5x + 6 and assumed this was between [-1/4, ∞] so inf = -1/4 and sup does not exist as it is not bounded from above.

    [tex] {x | x^2 + 1 = 0 } [/tex]
    as I'm in a real analysis class, there isn't a real number such that x^2 + 1 = 0, so inf and sup do not exist

    could anyone check my answers and if my reasoning is correct, especially for the second one please

    I don't understand why the curly brackets are not showing, but there should be curly brackets around all above in tex
  2. jcsd
  3. Oct 11, 2013 #2


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    Looks good.

    It's talking about the range, so yes, that looks right too.

    The curly brackets have a special use in TeX, so to display then you use \{ and \} as I did editing your first set.
  4. Oct 11, 2013 #3
    thank you for a fast reply,

    is the last one correct too as you did not comment on that?
  5. Oct 11, 2013 #4


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    I would say so as long as your text doesn't have some special convention for empty sets.
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