how to get trendlines with 3 variable inputs (x,y,z)

**Edwinywh** · 12-07-2020, 06:34 AM

Variable 'z' is a function of variable 'x' and 'y'.

I have the numerical values for x,y,z. I'm trying to get a trendline equation of it, preferably in polynomial form.
Any help would be appreciated.

**MrShorty** · 12-07-2020, 10:17 AM

Have you chosen a regression equation? What do you want your polynomial to look like? Are you familiar with the LINEST() function?

For a "polynomial" in 3 dimensions, the process I would expect to use:

1) Arrange raw data in a simple list with single columns for x, y, z.
2) Add helper columns to calculate each f(x,y) term.

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3) Use the LINEST() function (z column is the known_y argument and your block of fi(x,y) is your known_x argument) to perform the regression. LINEST() help file: https://support.microsoft.com/en-us/...a-fa7abf772b6d
4) Evaluate the regression.

Which step do you have trouble with?