how do i add an x-y convergence drop line from y to x axis?

[Paulc]

I have an excel graph where the x and y lines converge.
I want to be able to drop a line from that point to the x axis

Thanks, Paul.

 

[Jon Peltier]

Andy Pope shows how to get the intersection of two lines:

http://andypope.info/charts/intersection.htm

From the data point that is added at this intersection, use an error bar,
negative Y using 100% of the value, to draw the line to the axis.

- Jon