Why doesn't the equation correspond to the graphic?

[Guest]

Hi.
I drew a graph using some data. So I asked Excel to put the tendency curve
using a 5th degree polinomial. I also asked for the equation. The problem is
when I input the points into the equation the y values do not correspond to
the ones in the graph.
Can you help me? If necessary I can send you the file with the data.
Thanks.

 

[Guest]

The trend line equations displayed in Excel normally do not have sufficient
significant places to be used directly in an equation.
Select the trend line equation on the chart and change the format such that
there are more significant places.
(This has burnt me in the past, I always check by plotting the calculated
values on the chart with the trend line showing to insure I amm close enough.)

 

[Guest]

Hi, BJ.
Thanks for your fast answer. The points are: I don't know hoe to change
number of places for the coefficients. Besides, the difference is big. It's
not a matter of rounding. For example, in the graph the value is 8.4 and the
equation gives 11.0. Do you think is only a matter of places? So, how can I
change this?
Thanks a lot

 

[Guest]

look on the toolbars for a button that looks something like

.0
..00

or select the trend line equation <format><selected data labels><number>
and change the number in the decimal Places box

the 11 vs 8.4 is exactly the type of problem I had
a difference in significant figures will easily give this type of difference

 

[Guest]

BJ
You are right!! When I increased 1 place the result got much better.
Thanks a lot!!