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Polynomial Fit in EXCEL does not work as it should

  1. Apr 16, 2009 #1
    Hello all,

    I am trying to extract the 2nd degree polynomial coefficients from a curve of best fit applied in EXCEL. I know how to do it (http://spreadsheetpage.com/index.php/tip/chart_trendline_formulas)

    2nd Order Polynomial Trendline

    Equation: y = (c2 * x^2) + (c1 * x ^1) + b
    c2: =INDEX(LINEST(y,x^{1,2}),1)
    C1: =INDEX(LINEST(y,x^{1,2}),1,2)
    b = =INDEX(LINEST(y,x^{1,2}),1,3)


    Iv done it before, but for some reason it is not working out for my particular data set. I keep getting errors or zero for my coefficients. If I do the regular best fit using the trendline option, it works.

    I get: y = 2E+16x2 + 1E+11x + 3.033

    I am attaching my data set.

    Does any one know if there is something wrong with my method? Perhaps Im forgetting something.

    Thanks.
     

    Attached Files:

  2. jcsd
  3. May 19, 2009 #2
    You should pay attention to of the two columns represent Y and which represents X. I think you are reversing them between the trendline and the LINEST function.
     
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