how do i transpose a Polynomial equation from a graph to a sheet?

[All at Sea]

I have produced a polynomial trend line in a graph. I now want to produce
that curve but the equation provided on the graph does not produce it. Is it
possible for Excel to produce that equation for me directly onto a sheet and
thus enable me reproduce the curve so that I can then use the values in a
look up table? Help?

 

[David Biddulph]

If the equation doesn't seem to be producing the same as the trendline
you're seeing on the grpah, it's probably because you're not using enough
decimal places for your coefficients.

 

[Mike Middleton]

All at Sea -

One way to get the coefficients on a worksheet is to use the array-entered
LINEST function (Control+Shift+Enter). For a polynomial of order 3, use

=LINEST(y-range, x-range^{1,2,3})

One of the reasons that your equation may seem incorrect is you may be using
a Line chart type (which defaults to 1,2,3,... for the x values) instead of
an XY (Scatter) chart type (which uses the numerical x values).

Another reason for differences is that you may not be displaying enough
significant digits.

- Mike Middleton
http://www.DecisionToolworks.com
Decision Analysis Add-ins for Excel