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Homework Help: Annoying limit problem

  1. Oct 3, 2007 #1
    1. The problem statement, all variables and given/known data
    1/b - 1/3
    -----------
    b-3



    Lim b ----> 3


    2. Relevant equations



    3. The attempt at a solution


    This is driving me nuts. I always end with 0 but thats not the answer.
    I tried direct substitution and it didn't work.

    I tried plugging in 2.999999999 but it gives a very small number devided by a very small number

    I tried the conjugate and even deviding by the highest power altho thats for infinity.
     
  2. jcsd
  3. Oct 3, 2007 #2

    D H

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    Staff Emeritus
    Science Advisor

    You can try this experimentally to see what the limit (if any) appears to be. It takes less than a minute to set this up in an Excel spreadsheet .

    You can also try to simplify the expression. What is the numerator?
     
  4. Oct 3, 2007 #3
    I don't really see how further I can simplyfy

    numerator is

    1 devided by ''b' minus 1 devided by 3
     
  5. Oct 3, 2007 #4

    D H

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    Find the common factor.
     
  6. Oct 3, 2007 #5
    I don't see a common factor in

    1/b - 1/3

    or

    b-3
     
  7. Oct 3, 2007 #6

    dynamicsolo

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    Homework Helper

    How do you take the difference of two fractions?
     
  8. Oct 3, 2007 #7
    woa... nwo seriously how did I miss that. I wasted soo much time on this.
     
  9. Oct 3, 2007 #8
    well am still stuck.


    So I put them on the same denominator and end with


    (3-b) / 3 b
    -------------
    b-3
     
  10. Oct 3, 2007 #9
    okay -1/9 got it finally . thx for the help
     
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