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 ?