HP 39gs Master Manual page 61

Areas between and under curves
If we are wanting to find true areas rather than the 'signed areas' given by a simple definite integral then we
must take into account any roots of the function.
The difficulty with this is that for most functions the roots and intersections are quite unlikely to be whole
numbers and rounding them off will produce inaccuracies in the calculation.
There are ways to get around this and the process is shown in detail on page 75. Basically the trick is to find
each root in turn and use the
be used in the calculation to retain full accuracy.
Extremum
The final item in the
find relative maxima and minima for the graphs.
Ensure that is switched on and that the cursor is positioned on
the cubic in the vicinity of the left hand maximum (turning point)
F2(X)
as shown right. Press
should find that the cursor will jump to the position of the maximum.
Calculator Tip
If your graph has asymptotes then make sure that the cursor is
positioned on the side of the asymptote containing the extremum before
initiating the process. The internal algorithm used does not cope well
with intervening asymptotes.
view to store the values of the roots as
HOME
menu is the Extremum tool. This is used to
and choose Extremum from the menu. You
,
A
61
, ... These values can then
B C