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Proving using ε/δ definition

  1. Sep 14, 2013 #1

    cwz

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    1. The problem statement, all variables and given/known data
    Prove using ε/δ definition,

    lim x tends to -1 (x^3+2x^2) = 1


    2. Relevant equations



    3. The attempt at a solution
    I have done to the step where δ(δ^2-δ-1) ≤ δ ≤ ε

    so i choose ε=min(2,ε)

    Not sure whether I am correct or not
     
  2. jcsd
  3. Sep 14, 2013 #2

    vela

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    I hope you realize that
    $$\lim_{x \to -1} (x^3+2x^2) \ne 1$$ so you're going to have a tough time proving it. In any case, you need to show more of your work. We can't see your paper or read your mind to see what you actually did.
     
  4. Sep 14, 2013 #3

    pasmith

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    [itex](-1)^3 + 2(-1)^2 = -1 + 2 = 1[/itex]. Last time I checked, [itex]x^3 + 2x^2[/itex] was continuous everywhere.
     
  5. Sep 14, 2013 #4

    vela

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    Well, now I feel like an idiot. :wink: And I checked it over and over and kept getting -1.
     
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