HP 39g Master Manual page 169

The c coefficient is shown as a multiple of
decimal. The currently active coefficient is highlighted and can be changed
using the up/down arrow keys in increments of 0.1 for the coefficients a, b
and d.
The default increment for c is
be changed using the key labeled
π π
either or .
9 4
When in mode, the increments are 20
o o o
30 or 45 with 30
The ranges of values available for the four
coefficients are shown below:
Coeff. Range
-3 to 3
a
0.2 to 5
b
-4 π to 4
c
-3 to 3
d
If you go to HP's website you can download a worksheet for use with your
class. It takes the student through the process of deducing the effects of
each of the coefficients on the shape of the graph, requiring them to record
their answers in writing.
π
but this can
6
being the default.
π
169
π in radian mode rather than as a
to
o
,