# [SOLVED] How do i approximate the value of a point on the trendline?

1. ## [SOLVED] How do i approximate the value of a point on the trendline?

I created a polynomial trendline for a sales forecast. How do i figure out a
appriximate value for a point on the trendline

2. ## RE: How do i approximate the value of a point on the trendline?

Dheer,

Double-click on your trendline, go to Options -> Display Equation on Chart.
Once Excel displays the equation, substitute some number for X to calculate Y
to get a point value. Typically, you could substitute 1, 2, 3, 4, 5, 6, 7, 8
.. . . etc. for X to get a series of corresponding Y values. If you plotted
those XY values, they should mirror your trendline.

----
Regards,
John Mansfield
http://www.pdbook.com

"Dheer" wrote:

> I created a polynomial trendline for a sales forecast. How do i figure out a
> appriximate value for a point on the trendline

3. ## Re: How do i approximate the value of a point on the trendline?

Be certain to display the coefficients in scientific notation with 14
decimal places, otherwise you will get rounded coefficients that may not
produce good estimates with your data.

Alternately, you can use the LINEST() and TREND() worksheet functions to
estimate polynomials
http://www.stfx.ca/people/bliengme/E...Polynomial.htm
In Excel versions prior to 2003, LINEST uses a different algorithm that
may have more numerical problems with challenging data or high order
polynomials than the chart trendline.

Jerry

John Mansfield wrote:

> Dheer,
>
> Double-click on your trendline, go to Options -> Display Equation on Chart.
> Once Excel displays the equation, substitute some number for X to calculate Y
> to get a point value. Typically, you could substitute 1, 2, 3, 4, 5, 6, 7, 8
> . . . etc. for X to get a series of corresponding Y values. If you plotted
> those XY values, they should mirror your trendline.
>
> ----
> Regards,
> John Mansfield
> http://www.pdbook.com
>
>
>
> "Dheer" wrote:
>
>
>>I created a polynomial trendline for a sales forecast. How do i figure out a
>>appriximate value for a point on the trendline

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