Texas Instruments PLUS TI-89 - Manual (Page 147)

130 Chapter 7: Parametric Graphing
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 130 of 6
Use 3 to set Graph = PARAMETRIC before you define equations or
set Window variables. The Y= Editor and the Window Editor let you
enter information for the current
Graph mode setting only.
To graph a parametric equation, you must define both its x and y
components. If you define only one component, the equation cannot
be graphed. (However, you can use single components to generate
an automatic table as described in Chapter 13.)
Be careful when using implied multiplication with t . For example:
Enter: Instead of: Because:
t ù cos(60) tcos(60) tcos is interpreted as a user-defined
function called tcos , not as implied
multiplication.
In most cases, this refers to a nonexistent
function. So the
TI -89 / TI-92 Plus simply
returns the function name, not a number.
The Y= Editor maintains an independent function list for each Graph
mode setting. For example, suppose:
¦ In FUNCTION graphing mode, you define a set of y(x) functions.
You change to PARAMETRIC graphing mode and define a set of x
and y components.
¦ When you return to FUNCTION graphing mode, your y(x) functions
are still defined in the Y= Editor. When you return to
PARAMETRIC graphing mode, your x and y components are still
defined.
Differences in Parametric and Function Graphing
This chapter assumes that you already know how to graph y(x)
functions as described in Chapter 6: Basic Function Graphing.
This section describes the differences that apply to parametric
equations.
Setting the
Graph Mode
Defining Parametric
Equations on the
Y= Editor
Note: When using t, be sure
implied multiplication is valid
for your situation.
Tip: You can use the Define
command from the Home
screen (see Appendix A) to
define functions and
equations for any graphing
mode, regardless of the
current mode.
Enter x and y components
on separate lines.
You can define
xt1(t) through xt99(t) and
yt1(t) through yt99(t).