NumStart & NumStep
Retaining calculated values
When you find an extremum or an intersection, the point is remembered
until you move the cursor even if it is not actually on a value that would
normally be accessible for the scale you have chosen.
For example, if you find an intersection and then immediately return to
the
menu and choose
Slope
, the slope calculated will be for the
intersection just found rather than for the nearest pixel point. If you have
recently found a root then pressing the
key and entering the value
Root
will return the cursor to it.
There are two ways to access these values:
o
The first and simplest is via the value stored in memory
X
. If you move from the
PLOT
view to the
HOME
view without moving the cursor and type
X
then the value it will contain will be the last
position of the cursor. If you just found a root or an intersection then this will be the value displayed.
To find the y value for the x coordinate just evaluate
F1(X)
in the
HOME
view (or whatever function
you are using).
o
The second way is via the reserved words of
Root
,
Extremum
,
Area
,
Slope
and
Isect
. Typing
any of these reserved words in any situation will retrieve their last calculated values. If a value has not
yet been found then they will return zero.
This trick is particularly useful when calculating areas under or between curves. See page 75.
The NUM view revisited
We saw earlier that the
NUM
view gives a tabular view of the function.
It is possible to manipulate this view through the
NUM SETUP
view. The first way is to change the start value
and the step size for the view.
For example, values of 10 and 2 give:
70