Find the maximum of a regression line in Excell

[paulomanuel]

I have 4 points in a graph and i can find a tendencie line but when i try to find a 4th degree regression line with the parameters m1,m2,m3,m4 and b it turns out to be a very bad aproximation. I am trying to find the right equation in order to find its maximum.

Does anyone know what is the problem or if it is impossible to perform in Excell?

 

[Ari]

Hello,

Why use a 4th degree polynomial?

You could have a linear relationship with 4 points. I think you don't because you spoke of maxima.

Anyway, if you have 4 points, you can fit at the most a 3rd-degree polynomial (r=1 for this case)


Ari Constancio, Chem. Eng.
ari.constancio@netc.pt

http://www.terravista.pt/ancora/1588

 

[Ron]

Are you sure you're looking for a regression? It sounds more like you're looking for an inflection point (maxima). If that's the case, take the first derivative of the line connecting the points.

 

[paulomanuel]

Maybe I wasn't very explicit.
My problem is findind the regression line. I mean, a good regression line, because the ones that i tried weren't good aproximations.
Maybe it's not possible to be accurate with standard Excel functions.