tangent normal line..lots of goodies!
This simulation finds many different things.
1) derivative, graphs of tangent and normal lines
2) value of curve and f prime at a point
3) graphs curve, tangent line, normal line
4) gives nice symbolic and decimal forms of equations
5) allow you to turn things on and off in the right panel
6) you can zoom in and out..center on the point of tangency..
..others