Texas Instruments TI-89 Manual Book page 185

How Are Z Values
Determined?
Drawing a Contour
for the Z Value of a
Selected Point
Interactively
Tip: Any existing contours
remain on the graph. To
remove the default contours,
display the Window editor
( ¥ $ ) and set
ncontour=0 .
168 Chapter 10: 3D Graphing
You can set the
ncontour
number of contours that will be evenly distributed along the
displayed range of z values, where:
zmax ì zmin
increment =
ncontour + 1
The z values for the contours are:
zmin + increment
zmin + 2(increment)
zmin + 3(increment)
©
zmin + ncontour(increment)
If ncontour=5 and you use the standard viewing window (
and ) , the increment is 3.333. Five contours are drawn for
zmax=10
z=ë 6.666, ë 3.333, 0, 3.333, and 6.666.
Note, however, that a contour is not drawn for a z value if the 3D
graph is not defined at that z value.
If a contour graph is currently displayed, you can specify a point on
the graph and draw a contour for the corresponding z value.
1. To display the
Draw
2 ˆ
TI-89:
: ˆ
TI-92 Plus
2. Select
7:Draw Contour
3. Either:
¦
Type the point's x value and press
¸, and then type the y value
and press ¸.
– or –
¦
Move the cursor to the applicable point. (The cursor moves
along the grid lines.) Then press ¸.
For example, suppose the current graph is
specify x=2 and y=3, a contour is drawn for z=3.5.
Window variable ( ¥
The default is 5. You can
set this to 0 through 20.
menu, press:
.
z1(x,y)=xñ +.5yñ ì 5
$ ) to specify the
zmin=ë 10
. If you