How do I get the gradient at a point on a curved graph?

[Guest]

I have a plot of experimental data and I inserted an exponential trendline
that fits the data very well. I'd like to "differentiate" the curve as I need
its gradient at certain points; as in I need Excel to draw the tangent to the
trendline at a given point and tell me its equation. Can anyone help me do
this?

Thank you all so much.

 

[MrShorty]

I don't think Excel knows how to do this as a built in thing. Extract
the coefficients of the trendline to a worksheet (using a worksheet
function such as LOGEST or a utility that will extract trendline
coefficients to a worksheet). Then you can use the coefficients and
your knowledge of calculus to determine a formula for the slope of the
function at any point. Then use that formula to put together a series
of data points that you can plot as the tangent of the curve.

 

[Guest]

thanks loads, i'll try it out