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Homework Help: Quick question about domain

  1. Feb 18, 2008 #1
    1. The problem statement, all variables and given/known data

    I have to do a few graphs and some equations with certain domains but I've never seen the domain written in this way:


    Usually I see the domain written with something like 2<x<4. What exactly does the above mean?
  2. jcsd
  3. Feb 18, 2008 #2


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    [itex]x\in (-\infty,2] [/itex] means [itex]-\infty<x\leq 2[/itex] and [itex]x\in(2,\infty)[/itex] means [itex]2<x<\infty[/itex]
  4. Feb 18, 2008 #3
    2+ means go to near 2 from the right side (from number greater than 2) and 2- means go to near 2 from number less than 2 which means the left side

    OK, now in here when you want to find the limit of the function because you have a discontinued in 2 (the value of your function is different in left and right of 2) the limit is different wile you look it from left of 2 or right of 2,

    the key point is try to find the limit of f from 2+ from the function that is valid in (2,oo) and try to find the limit of f from 2- from the function that is valid in (-oo, 2]
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