On Tue, 18 Sep 2007, in microsoft.public.excel.charting,
mark said:

how can i draw a tangent line on a graph with a curve of best fit?

Use algebra in the spreadsheet to construct both the curve and the
tangent, then use an XY (Scatter) Chart type to present them on a graph.
Don't use the built-in Trend Line facility in charts, because then you
won't be able to work out for yourself what the tangent is.

--
Del Cotter
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