Excel : Tangent to a curve

This seemed like a simple problem...

I need to graph the tangent to a curve that is given by data point in Excel. How do I do that?

thanks.

To do that mathematically:

(1) Find the slope, or for a curve, the derivative at point (x).

(2) Find the (x,y) at point (x) where the tangent "touches" the curve.

(3) The equation for the tangent line is y = mx + b,

where m = derivative at point x, and b = y - mx, where (x,y) are the point at which tangent touches the curve.

You cannot make a tangent to any single point, or more specifically, 1 point has an infinate number of tangents.

If you want an approximate to your request, you need 3 points.

-Lou

What I'm saying is that from some data points, I can construct a curve of best fit (well, excel does it for you). From that it would seem that it should easily be able to draw tangents to any point on the curve. But as far as I can tell, there is no functionality that does that.

I'm waiting for someone to prove me wrong here.:)

I'm assuming what you're asking is if there is a built-in function that will do that. I don't think there is.

Which seemed rather stupid to me. Doesnt anyone ever use excel for anything that requires you to know derivitives of functions that are only defined based on data points? whatever.