Trend Line constants as Excel Cell Values

[Ken]

I want to put the constants of a 2 degree polynomial trend line into Excel
Cells. Are there formula's to do this? Equation is Y = Ax(2) + Bx + C. I want
the value of A,B and C in seperate cells. Can anyone suggest how this can be
done? Thanks

 

[B. R.Ramachandran]

Hi Ken,

Supposing your x-range is in A2:A10, and y-range in B2:B10,

select a 3-column x 1-row area and enter the following formula and confirm
with CTRL-SHIFT-ENTER.

=LINEST(B2:B10,A2:A10^{0,1,2},0,)

Regards,
B. R. Ramachandran

 

[Ken]

Thanks B. R.Ramachandran again for your great assistance. Ken

 

[Andrew]

How would this work for a Polynominal degree 6? X-range covers 52 points.

 

[B. R.Ramachandran]

Hi Andrew,

Let's suppose that the x- and y- ranges are in A2:A53 and B2:B53 respectively.
Select a 7 column x 1 row area, enter the following formula, and confirm
with CTRL-SHIFT-ENTER.

=LINEST(B2:B53,A2:A53^{0,1,2,3,4,5,6},0,)

The formula will return the 7 coefficients, starting from the zeroth order
and ending with the 6th order.

If you want to have the coefficients shown starting from the 6th order and
ending in the zeroth order, modify the formula as,

=LINEST(B2:B53,A2:A53^{6,5,4,3,2,1,0},0,)

Regards,
B. R. Ramachandran

 

[gdors]

Very nice solution! Is there a way to present the resulting coefficients in
the same column as the data? Or, better yet, to predict the value of Y from a
New X and known Xs and known Ys that fit well to a polynomial?

 

[Jerry W. Lewis]

To put all the coefficients in a column, use the TRANSPOSE function.

To get predicted Y values, use the TREND function. For this model, the
syntax is
=TREND(B2:B53,A2:A53^{0,1,2,3,4,5,6},prediction_x_vals,0,)
If you just want the predicted values for the original data, you can omit
the third argument
=TREND(B2:B53,A2:A53^{0,1,2,3,4,5,6},,0,)

Jerry

 

[Doublee]

If you are trying to solve for x knowing all the other terms, rearange the
equation:
x^2+Bx/A +C-Y =0 to ax^2+bx+c=0
Then use the solution for the roots:
(-b+-sqrt(b^2-4ac))/2a