# Polynomial Fit in EXCEL does not work as it should

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.

#### Attachments

• data.txt
1.4 KB · Views: 261

## Answers and Replies

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.