> I intended to clarify the idea. Apparently, I failed.
>
> I assumed, when creating the posting, that my audience could visualize
> tangent lines to curves and tangent planes to spheres/surfaces [NOT
> compute them!]...
That much I can do.
> Do you want me to try again? I think a more pictorial approach would
> have a better chance. The concept can almost entirely be explained
> graphically.
>
If you would.
Take care. -KMO