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Homework Help: A Question about the Domain and Range of a Function

  1. Sep 28, 2013 #1
    1. The problem statement, all variables and given/known data

    I constructed my own question to try to make sense of the following notation.

    g(x) = 2√x g : X → Y. What does X and Y equal?

    2. Relevant equations

    For 2√x, x = or > than 0.

    3. The attempt at a solution

    g(x) = 2√x g : [0, ∞) → [0, ∞)

    So X = Y = [0, ∞)

    The reason why I am doing this is because my book shows this: g(x) = 2√x g : [1,∞) → [2,∞). Why does my book have a 1 instead of a 0 as an initial x value?
    Last edited: Sep 28, 2013
  2. jcsd
  3. Sep 28, 2013 #2


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    You have found the LARGEST domain that that function can be defined on. X could always be defined to be a subset of that domain, in which case your job is to figure out the corresponding Y. Are you sure the book didn't tell you X=[1,∞)??
  4. Sep 28, 2013 #3
    The book just shows this, "g(x) = 2√x g : [1,∞) → [2,∞)" as an example of, "g : B → C". I just used X and Y for this thread.
  5. Sep 28, 2013 #4


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    The book could also have said correctly that "g(x) = 2√x g : [4,∞) → [4,∞)". That would work also, right? Nothing in the problem really fixes what X HAS to be.
  6. Sep 29, 2013 #5
    Oh, I see, thank-you!
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