A learning curve is as it sounds the phenomenom of the time required to fulfill certain tasks decreases with increasing repetitions. The formula is Tn = T1 * n^b
Tn=Time for nth unith
T1 = Time for first unit
b= ln (learning percent) / ln 2
Well, what you're asking is quite different to what appeared in your first post. From memory, you should be able to switch the graphing mode to sequence in mode and then enter the above expression. It's been a long time since I used a TI-84 (I upgraded to the TI-91 some time ago). The you can graph it, examine tables etc.