https://bugs.documentfoundation.org/show_bug.cgi?id=105427
--- Comment #6 from GerardF <gerard.farg...@orange.fr> ---
(In reply to andi from comment #5)
> - no matter if chosen "curve" or "line" chart the resulting formula is wrong!
>
> - mathematical background: to approximate 3 given x/y points the resulting
> formula with second square polynom finds all these given points exactly!!!
>
> - the correct resulting formula for the 3 points (-2/4) (0/0) (2/4) would be
> y(x)=x²
>
> - the wrong trendline formula found by calc is: y(x) = 4x²-16x+16
> - try with (0/0); does y(x)=4x²-16x+16 hit (0/0)? No!
> - does y(x)=x² hit (0/0) Yes!
As said in the help, with a line chart, trendline equation use 1, 2, 3... as X
points.
So your 3 points are not (-2/4) (0/0) (2/4) but (1/4) (2/0) (3/4) and (2/0)
gives 4*2^2-16*2+16 = 0
If there is a bug here, he is in the help. (not enough explicit)
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