HP 39g hp 39g+ (39g & 40g)_mastering the hp 39g+_English_E_F2224-90010.pdf - Page 148

Using Stats to find equations from point data, Quadratic, Auto Scale, Exponential

Page 148 highlights

Using Stats to find equations from point data eg. 1 Find the equation of the quadratic which passes through the points (1,5), (3,15) and (-5,71). In the Statistics aplet, choose mode and enter the data. Now change to the SYMB SETUP view and choose the Quadratic data model. Change to the PLOT view using the VIEWS Auto Scale option and press the key. Don't worry that the scale is not good because we don't care about the graph. It only needs to be drawn in order to calculate the fit equation. Finally, change back to the SYMB view and see the equation, pressing if necessary. eg. 2 A population of bacteria is known to follow a growth pattern governed by the equation N = N0ekt ;t ≥ 0 . It is observed that at t = 3 hours, there are 100 colonies of bacteria and also that at t = 10 hours there are 10 000 colonies. (i) Find the values of N0 and of k. (ii) Predict the number of bacteria colonies after 15 hours. (iii) How long does it take for the number of colonies to double? (i) Find N0 and k. Start up the Statistics aplet, set it to and enter the data given. Change to the SYMB SETUP view and specify an Exponential model for the data. 148

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148
Using Stats to find equations from point data
eg. 1
Find the equation of the quadratic which
passes through the points (1,5), (3,15)
and (-5,71).
In the Statistics aplet, choose
mode and
enter the data. Now change to the
SYMB
SETUP
view and choose the
Quadratic
data
model.
Change to the
PLOT
view using the
VIEWS
Auto Scale
option and press the
key.
Don²t worry that the scale is not good because
we don²t care about the graph. It only needs to
be drawn in order to calculate the fit equation.
Finally, change back to the
SYMB
view and see
the equation, pressing
if necessary.
eg. 2
A population of bacteria is known to follow a growth pattern governed
by the equation
0
;
0
kt
N
Ne
t
=
.
It is observed that at t = 3 hours, there are
100 colonies of bacteria and also that at t = 10 hours there are 10 000
colonies.
(i)
Find the values of
0
N
and of
k
.
(ii)
Predict the number of bacteria colonies after 15 hours.
(iii)
How long does it take for the number of colonies to double?
(i)
Find
0
N
and
k
.
Start up the Statistics aplet, set it to
and enter the data given.
Change
to the
SYMB
SETUP
view and specify an
Exponential
model for the data.