Trendline equation

Trendlines and LINEST compute coefficients in different ways, for some reason that escapes me, so I don't have a suggestion for that.

However, there is no need to invoke LINEST (a very heavyweight function) four times to get four coefficients. Select a range 4 columns wide, and paste this in the formula bar:

=LINEST(C2:C7, B2:B7^{1,2,3})

Don't press Enter; instead, press and hold the Ctrl and Shift keys, then ppress Enter.

Thanks, shg. That is what I thought about it. Is there some other way to get the coefficients without using LINEST function and be able to show even the smallest numbers?

You could do your own matrix inversion, but why bother? The numbers are negligably different, considering the dynamic range of the coefficients, and the fact that you're doing a basis-function (here, polynomial) fit, which is, by definition, an approximation of an over-defined system.

Mmmh...Ok, shg. Let me see then what to do on the matter. Thanks a lot.