Solver Root

[PEcomStock]

I created a trendline and associated equation for some data plotted against Time on the x-axis displayed in MM/DD/YY format. The date for the data ranges from 3/27/06 thru 11/10/08.

The trendline equation is…

F(x)=-6E-13x^5+1E-07x^4-.0087*x^3+329.1*x^2-6E+06*x+5E+10

The data actually crosses the y=0 line around 11/5/07, which is the data root

When I use Goal Seek, I got a zero root solution of 28154.98. When I convert this to the date format, it converts to a date in 1981 which is not correct. I tried a range of initial guesses but they all converge to the same number.

Any suggestions what the problem is?

 

[pgc01]

It strikes me that Microsoft could modify their program to automatically rescale the x axis by subtracting the lowest value(X1) from each x-value and then adding back the X1 to the polynomial

I agree that Microsoft should make the statistical area reliable. This has been a week area for a long time.

What can I do in appreciation? I don't know the procedure here…

You have experience with excel and competence in mathematics. You could hang out here now and then, and share yout knowledge helping others.

Cheers.

 

[PEcomStock]

PGC, I will try and help though I don't consider myself and expert on Excel.