Looking for prediction using quadratic curve fit

[Dick]

I am looking for a something like the Excel FORECAST
function, except it should work for a quadratic equation
instead of linear equation. I already understand how to
use the Excel quadratic line fitting formula to get the
coefficients (a,b,c) in y = ax^2+bx+c. What I want to
know is how to predict a value for the next interval (next
x-value) based on the formula without having to fill in
the x-value into the equation.

 

[Bernard V Liengme]

Hi Dick,
Let's say you x-values are in A2:a11 and y-values in B2-B11
You can find the parameter a, b and c thus; select three cells in a row,
enter =LINEST(B2:B11,A2:A11^{1,2}) and complete the formula with
CRTL+SHIFT+ENTER since it is an array formula.
Now you have the parameters, predicting y-values for other x-values is
simple math. But beware of extrapolating too far.
best wishes
Bernard
www.stfx.ca/people/bliengme