Tracing the integral in PLOT
key, an alternative method is to use the
tracing facility. The advantage of this is that the ‘area’ is shown visually
as you go by shading, as can be seen right.
Rather than using the
The disadvantage of this is that you can only trace to values which are permitted in the scale you are using.
As soon as you use
the shading stops. In this case, due to the scale we chose, if you try to trace to the
values x = -3 or x = 2 you will find that they are not accessible. To
illustrate the process we will need to change scale.
Change to the
PLOT SETUP
view and set the x axis (only) back to the
default values
-6.5
to
6.5
, then
PLOT
again. This can be done by
highlighting the
XRng
fields and pressing
DEL
.
and
again, choosing
Signed Area…
as before. Use
the left/right arrow keys or the
Press
key to move the cursor to x = -2.
Press
ENTER
to accept the starting point.
This time, choose the boundary as
F2(X)
instead of the x axis so that we
will be finding the signed area between curves instead of the signed
area under one. Again, note that the result will be a signed area
(definite integral) not a true area. See page 75 for a simple method of
finding true areas.
We now need to choose the end point. This time do it by tracing with
right arrow to move the cursor. As you do the area will be shaded by
the calculator. The current position is shown at the bottom of the screen.
When you reach the end point you are looking for, press the
key
and the area will be calculated as before. This is shown right. To
remove the shading, press
PLOT
again to force a re-drawing of the
screen.
Calculator Tip
certainl
calculator.
as 0.5
Common sense tells us that the answer in the example above is almost
y -3.75 rather than -3.75000000002. The small error is simply
due to accumulated rounding error in the internal methods used by the
For example, an answer of 0.4999999999 should be read
This is quite common and users should be aware of the need
for common sense interpretation.
60
