If your equation is from the chart display, then by default the coefficient
values will be too heavily rounded to use. Right click on the dilpayed
equation and format in scientific notation with 14 decimal places. Also make
sure that your chart is an "XY (Scatter)" chart and not a "Line" chart.

You may not have a broad enough range of x-values to permit accurate
numerical calculation of the coefficients (is the data set small enough to
include in the body of a reply?). This can be especially problematic if your
polynomial coefficients are from LINEST() in Excel versions prior to 2003.
In 2003's LINEST, coeffients of exactly zero are also suspect.

Jerry

"Mauro" wrote:

I have a serie of experimental data (x1,...xn) and (y1, ..., yn). I plote the
points on an XY chart and I try to fit the trendline. The equation of this
trendline is like the following: f(x)=a*x^6 + b*x^5+c*x^4+....+h. But when i
evalute the function f(x) in the each value of x, f(xi) I obtained a linear
function that is different from the data tendency. What i am doing worng or
how can i get the correct function of the plot.

The plot of the experimental data is like the nromal distribution, and I
need to obtain the area under the peak ? Is there any function on the excel
that permits this ?