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Cant find the equation of thi line

  1. May 6, 2007 #1
    urgent..cant find the equation of thi line

    this is a home work assig for tomorrow

    i have a set of points on a graph....which makes a curve...the points are in huge numbers...it represents the focal length etc plz help me...i need to find an equation for that curve.....

    here is the file with graph
    http://files.filefront.com/New_Microsoft_Office_Excetxls/;7447761;/fileinfo.html
     
    Last edited: May 6, 2007
  2. jcsd
  3. May 6, 2007 #2

    HallsofIvy

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    What??? Pretty much nothing you have said here makes sense! How can we help you do anything if we have no idea what curve or what points you are talking about? How does a curve "represent" a number?
     
  4. May 6, 2007 #3
    sir i will tell you in detail

    i have a set of points.....

    which i plot on a graph....and i get a line which is lil bit curved

    the problem is i need to find an equation for this line...

    and i dont know which theory or what to do..
    plz do help
     
  5. May 6, 2007 #4

    Office_Shredder

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    Do you know what kind of graph it's supposed to be? Can you tell us what the points are? Do you know the context in which these points were determined?

    Basically, you've given us no information here
     
  6. May 6, 2007 #5
    i will give you in full detail...i will upload the graph now
     
  7. May 6, 2007 #6
  8. May 6, 2007 #7
    Could you just list the coords of the points?
     
  9. May 6, 2007 #8

    Office_Shredder

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    From first glance it appears to be some sort of x-r for r some positive number.... you can actually get excel to give you a trendline, but the equation isn't nearly as good as one could want. It's actually probably more like 1/(x+k) for some k a constant
     
  10. May 6, 2007 #9
    Seems quite linear to me, y = -0.000026704286*x+1.5329355 gives deviations of (in absolute value)

    0.001906192
    0.000880503
    0.000652092
    0.000377772
    0.000542125
    0.001377028
    0.001465157
    0.001604714
    0.000448685
    0.001621043

    This gives an average deviation of 0.001087531, quite a small value.
     
  11. May 6, 2007 #10
    If you want to get really accurate, the rational function

    (6878435.6+633131.5*x)/(1+425906.02*x+(-1.3161499)*x^2)

    gives really good results, with an average deviation of 0.00031

    Edit; I used Graph, a free and useful program, you can download it at

    http://www.padowan.dk/graph/
     
    Last edited: May 6, 2007
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