Help with Polynomial Equation

[WE5T]

Hello,

I am hoping someone can help me. I am looking to calculate the terms for a Third Order Polynomial that will allow me to calculate the Y value for a given X.

I have uploaded a spreadsheet that details what I am after in a little more detail.

Thanks in advance,

Andy

[MrShorty]

If this is a rare or one time thing, simply hand enter the coefficients of the polynomial into 4 convenient cells in the spreadsheet. Then build a suitable formula in C19 and copy it down. This could be =cell1*B19^3+cell2*B19^2+cell3*B19+cell4. With a cubic polynomial or higher, I often use the SERIESSUM() function =cell4+SERIESSUM(B19,1,1,cell1:cell3) https://support.office.com/en-us/art...4-96c49087f637 Be sure to format the formula text in the chart to display all significant figures to avoid errors from too few sig figs in some of those terms. Also, pay careful attention to relative and absolue references so the formula will be easy to copy.

If this is something you will do frequently, I would suggest you learn how to perform these polynomial regressions using the LINEST() function. There is an example of entering the LINEST() function for a cubic polynomial in the help file (just before the examples start): https://support.office.com/en-us/art...a-fa7abf772b6d

[micsza]

Well, I haven't delved into the problem but if that's cubic polynomial how does the simple linear regression seem to fit here?

[shg]

Because "linear" in linear regression means "linear in its solved coefficients," which polynomials are.

[micsza]

Yup, I was referring to "simple" not being aware LINEST() is more clever than this, thank you.

[shg]

It's not more clever; LINEST just sees multiple x variables, unaware that they are powers of a single variable.