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Chapter 7: Parametric Graphing 131
07PARAM.DOC TI-89/TI-92 Plus: Parametric Graphing (English) Susan Gullord Revised: 02/23/01 10:56 AM Printed: 02/23/01 2:13 PM Page 131 of 6
To graph a parametric equation, select
either
its
x
or
y
component or
both
. When you enter or edit a component, it is selected
automatically.
Selecting
x
and
y
components separately can be useful for tables as
described in Chapter 13. With multiple parametric equations, you can
select and compare all the
x
components or all the
y
components.
You can set the style for either the
x
or
y
component. For example, if
you set the
x
component to
Dot
, the
TI
-
89 / TI
-
92 Plus
automatically
sets the
y
component to
Dot
.
The
Above
and
Below
styles are not available for parametric
equations and are dimmed on the Y= Editor’s
Style
toolbar menu.
The Window Editor maintains an independent set of Window
variables for each
Graph
mode setting (just as the Y= Editor
maintains independent function lists). Parametric graphs use the
following Window variables.
Variable Description
tmin, tmax
Smallest and largest
t
values to evaluate.
tstep
Increment for the
t
value. Parametric equations are
evaluated at:
x(tmin) y(tmin)
x(tmin+tstep) y(tmin+tstep)
x(tmin+2(tstep)) y(tmin+2(tstep))
... not to exceed ... ... not to exceed ...
x(tmax) y(tmax)
xmin
,
xmax
,
ymin
,
ymax
Boundaries of the viewing window.
xscl
,
yscl
Distance between tick marks on the x and y axes.
Standard values (set when you select
6:ZoomStd
from the
„
Zoom
toolbar menu) are:
tmin = 0.
xmin =
ë
10. ymin =
ë
10.
tmax = 2
p
(6.2831853... radians
or 360 degrees)
xmax = 10. ymax = 10.
tstep =
p
/24 (.1308996... radians
or 7.5 degrees)
xscl = 1. yscl = 1.
You may need to change the standard values for the
t
variables
(
tmin
,
tmax
,
tstep
) to ensure that enough points are plotted.
Selecting
Parametric
Equations
Selecting the
Display Style
Tip: Use the Animate and
Path styles for interesting
projectile-motion effects.
Window Variables
Note: You can use a
negative tstep. If so, tmin
must be greater than tmax.