Re: Trendlines

On Sun, 18 Mar 2007, in microsoft.public.excel.charting,
Joel <Joel@xxxxxxxxxxxxxxxxxxxxxxxxx> said:
"Josh" wrote:
I used the trendline feature in excel and recieved an equation of "y =
3E+09x6 - 7E+08x5 + 8E+07x4 - 4E+06x3 + 42077x2 + 1197.x"

What do thhe Plus signs mean after the E (presumably the E means times ten
to the ____). Also, what does the decimal mean before the x (the last term)

below is the polynomial that represent the graph. Where ** means Raised to
the Power. x represent the x-axis on the graph. Below I tried to break out
the formula so you can understand it better. If you take a value on the
x-axis a added to the formular you will get approximately the value on the
y-axis

10**9 = 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10
3*(10**9) = 3000000000 : a 3 followed by 9 zeros
-7*(10**8) = -700000000 : -7 dollowed by 8 zerro

You didn't explain what the plus sign meant. All it means is that it could have been a minus instead. A minus makes the E mean "divided by ten to the ____", instead of "times ten to the ____"

1E+2 = 1*10^2 = 100
1E+1 = 1*10^1 = 10
1E+0 = 1*10^0 = 1
1E-1 = 1/10^1 = 0.1
1E-2 = 1/10^2 = 0.01

The numbers can be formatted so that the plus sign doesn't appear, and the minus sign only appears if there actually is a need for it. That would be a better format for displaying polynomial equations in trendlines. Just right click on the trendline equation, select "Format Data Labels" (that's just the trendline equation they're talking about) and make the required changes.

I haven't got an explanation for the decimal, as I can't get it to do that.

--
Del Cotter
NB Personal replies to this post will send email to del@xxxxxxxxxxxxxxxxxx,
which goes to a spam folder-- please send your email to del3 instead.
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