Polynomial Trendline

[tiltz]

I am using a polynomial trendline to project sales based on volume. When I switch the axis on the graph (for projecting volume based on sales) I get this trendline equation: y = 1E-09x2 + 0.0041x + 636.28. What is -09x^2?

The inverse function works perfectly (y = -0.0027x2 + 180.4x + 9415.8)

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[pgc01]

... I get this trendline equation: y = 1E-09x2 + 0.0041x + 636.28. What is -09x^2?

I guess you mean what is 1E-09

1E-09 = 1*10^(-9) = 0.000000001

 

[Asala42]

1E-09 is your coefficient for Xsquared, but it's showing as a very small number. You just need to show more decimal places to view the longhand.

In 2010, right click on the formula box>Format Trendline Label>Number>whatever decimal places you like.

 

[tiltz]

Here is the formula I am using, but the equation is not matching the graph when I put in sample X values (AD44) : =(EXP(-9)*AD44^2)+(0.0041*AD44)+636.28.

For example X=1M should return ~y=6000.

 

[shg]

You're only using 1 digit of precision. If you want to see the coefficients accurately, select a 3-cell wide range and array-enter*,

=linest(y, x^{1,2})

replacing x and y with references to the ranges where those values appear, e.g,.

=linest(B1:B10, A1:A10^{1,2})


*meaning confirmed with Ctrl+Shift+Enter rather than just Enter

 

[tiltz]

So how do I tie that function back to the original?

 

[shg]

The first value is the coefficient of x^2, the second is the coefficient of x, and the third is the constant.