
149
Either use the
VIEWS
Auto Scale
option, or
change to the
PLOT
SETUP
view and adjust it
so that it will display the data. This is not really
needed, since the line of best fit is what we
need and it will be calculated even if the data
doesn’t show.
Now change to the
PLOT
view and press
.
Wait while the line draws.
Change to the
SYMB
view, move the highlight
to the equation of the regression line and press
. Rounded to 4 dec. places, this gives an
equation of
0 6579
13 8950
t
N
e
⋅
= ⋅
.
(ii)
Predict N for t = 15 hours.
Change to the
HOME
view and use the
PREDY
function or use the facilities in the
PLOT
view.
Result: 268 269 colonies.
(iii) Find
t
so that
0
2
N
N
=
.
The value of
0
N
is the y intercept of the line of
best fit. These values from the curve of best fit
are not directly accessible but can be retrieved
using the
PREDY
function (see page 145). This
is shown in the screen shown right. Store the
results into memories A and K. This saves
having to re-type them from the
screen.
Now switch to the Solve aplet and enter the
equation to be solved. Changing into the
NUM
view, you should find the values of A and K
already defined (that was why we stored the
curve values into the appropriate memories),
so move the highlight to T and press
.
Result: Doubling time is 1.0536 hours.