Does anyone in this mailing list know what equation gets that 3d graph that is associated with the TI-89? If you don't know what graph I'm talking about, go to www.ticalc.org's website, and in the top left hand corner, there is a picture of the calc with the 3d graph on it. Anytime the TI-89 is shown in a picture (online or not), it is shown with this graph on the screen. Anyone have an idea as to the equation?