HP 39gs_40gs_Mastering The Graphing Calculator_English_E_F2224-90010

9
T
T
H
H
E
E
E
E
X
X
P
P
E
E
R
R
T
T
:
:
W
W
O
O
R
R
K
K
I
I
N
N
G
G
W
W
I
I
T
T
H
H
F
F
U
U
N
N
C
C
T
T
I
I
O
O
N
N
S
S
E
E
F
F
F
F
E
E
C
C
T
T
I
I
V
V
E
E
L
L
Y
Y
Finding a suitable set of axes
This is probably the most frustrating aspect of graphical calculators for many users and there is unfortunately
no simple answer. Part of the answer is to know your function – this is why we still expect you to learn
mathematics instead of expecting the calculator to do it all! If you know, for example, that your function is
hyperbolic then that immediately gives information about what to expect. If you don’t have knowledge then
here are a few tips:
•
give you a rough idea of how to ad
Try plotting the function on the default axes. You may find that enough of the function is showing to
just them to display it better. Remember that
can work on
either axis or on both. When in doubt, zoom out rather than in. See Tip #4 on the next page.
• The NUM view can be very helpful. Try changing to NUM SETUP and setting the value of
NumStep to 5 or even 10. Now scroll through the NUM view and look at what is happening to the
F(X) values. Look for two things.
o Firstly, where is the function most active? For what domain on the x axis is it changing rapidly
both up and down? This is likely to be the domain you are most interested in.
o Secondly, what is the range? What sort of values will you need to display on the y axis?
Change to the
PLOT SETUP view and set what you think may be appropriate axes. From
those you can
PLOT and then zoom in or out.
• If the graph is part of a test or an examination then the wording of the question will often give a clue
as to what x axis domain you should work with. You can then use Auto Scale.
Auto Scale can be used to get a first approximation to a good set of axes. To do this you must choose your x
axis domain first. Use your knowledge of what the function might look like, perhaps together with a quick
scroll through the
NUM view, to get an idea of what section of the x axis is important.
()
=
−100
+ 50
e
−0.025 x
For example, suppose a company’s profit is modeled by the equation
Px , where x is the
x
number of items manufactured. Suppose that from the context of the question it is clear that we are mainly
interested in the domain
0 ≤≤x 100 .
After entering the equation into the
SYMB view, change into the NUM
SETUP
view and set the numeric scale to start at zero and increment in
steps of 10 (or 5 if you want more details).
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