Tips & Tricks - Function; Finding A Suitable Set Of Axes - HP 39g Master Manual

T & T
T & T
I P S R I C K
I P S R I C K

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. 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:
1. Try just plotting the function on the default axes. You may find that
enough of the function is showing to give you a rough idea of how to
adjust them to display it better. Remember that ZOOM can work on
either axis or on both. See Tip #4 on the next page.
2. The NUM view can be very helpful. Try changing to NUM SETUP and
setting the value of NumStep to 1, or even 5 or 10. Now scroll
through the NUM view and look at what is happening to the F(X)
values. Look for two things.
Firstly, where is the function most active? For what domain on the x
axis is it changing fastest? This is likely to be the domain you are most
interested in.
Secondly, what is the range? What sort of values will you need to
display on the y axis?
Now 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.
3. 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.
4. I most often use Auto Scale to get a first approximation to a good set
of axes. To do this you must choose your x axis domain first so try Tip
#2 above and use your knowledge of what the function might look like.
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