Using an Equation from a trendline in a worksheet

[Daryl Nish]

Can anybody please tell me how can I use the equation from
a trendline in a cell on a worksheet. I know I can copy
the label from the text box but is there a function that
can return this equation on the worksheet in a cell??

 

[Bernard Liengme]

What type of trendline?
If linear use SLOPE and INTERCEPT' also look at TREND and FORECAST
If polynomial use LINEST; see example at
www.stfx.ca/people/bliengme/ExcelTips

 

[Daryl Nish]

Thanks Bernard, The raw data used to define the graph
isn't the equation I need, I'm after the equation of the
polynomial which is based on the actual data as drawn in
the trendline. Can I access this formula in excel?

Thanks Daryl

 

[Jerry W. Lewis]

As Bernard noted, the equation of a 1st order polynomial is computed by
SLOPE and INTERCEPT; the equation of higher order polynomials are
computed by LINEST (Help for linest is misleading, see Bernard's link).

Also on the Options tab of Chart|Add Trendline there is an option to
display the equation.

In Excel versions prior to 2003, the formula used by the worksheet
functions, while mathematically exact, can become inaccurate due to
numerical difficulties. The Chart equation has numerical properties in
all versions. If you don't have Excel 2003, compare the the output of
LINEST to the equation displayed on the chart as a check for whether
your problem is numerically challenging.

Jerry