# a function of the form f(t) = A exp( - k x ) where A and k are positive
# constants is called exponential decay. Exponential decay is a `good'
# model for many thinks including radioactivity and coffee cooling towards
# a constant (zero) room temperature.
#
#
# We are going to use ti-89 to fit data that `looks' like exponential
# decay. There are two methods here, but first lets load some sample 
# data: x in C1, y in C2
x   y
1   33
2   16
3   8.3
4   4
5   2
6   1
# after entering the data into the data editor one calculates
F5 (calculate menu)
type -> ExpReg
x is C1
y is C2
storeReg to y1(x)
enter
# this pops up a menu with
# y = a*b^x
#   a = 65.970956
#   b = .497284
#
# set up graphing window