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 = ë10. ymin = ë10.
tmax = 2p(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.