Texas Instruments TI-89 Guide

TI-89 Guide TI89-9
Copyright © Houghton Mifflin Company. All rights reserved.
values into the equation that is being graphed. We again assume that you have the function v(x)
= 3.622(1.093
x
) entered in the y1 location of the Y= list.
With the graph on the screen, press
F3 [Trace], press and hold
► to move the trace cursor to the right, and press and hold ◄
to move the trace cursor to the left. Again, note that the number
corresponding to the location of the equation (in the
Y= list) that
you are tracing appears at the top right of the graphics screen.
Trace past one edge of the screen and notice that even though
you cannot see the trace cursor, the x-andy-values of points on
the line are still displayed at the bottom of the screen. Also note
that the graph scrolls to the left or right as you move the cursor
past the edge of the current viewing screen.
Use either ► or ◄ to move the cursor near x = 15. We
estimate that y is approximately 13.7 when x is about 15.
It is important to realize that trace outputs should never be given
as answers to a problem unless the displayed x-value is
identically the same as the value of the input variable.
1.1.5 EVALUATING OUTPUTS ON THE HOME SCREEN The input values used in the eval-
uation process are actual function values, not estimated values such as those generally obtained
by tracing near a certain value. Actual values are also obtained when you evaluate outputs from
the graphing screen using the process that was discussed in Section 1.1.3 of this Guide.
We again consider the function v(t) = 3.622(1.093
t
) that is in Example 4 of Section 1.1.
Using x as the input variable, have
3.622(1.093)^ x entered in y1.
Return to the home screen by pressing HOME . Substitute 15
into the function with
Y 1(15 ) and find the function value
by pressing
ENTER .
NOTE: We choose y1 as the function location most of the time, but you can use any of the
available locations. If you do, replace
y1 in the instructions with the function you choose.
It is now a simple matter to evaluate the function at other inputs.
For instance, substitute x = 20 into the equation by editing the
entry line using
► , changing 15 to 20 by pressing   
and typing 20 ) , and then pressing ENTER . Evaluate y1 at 0
using the same procedure.
If you defined the function v with input t (see the bottom of page
C-6), it can easily be used to find the function outputs.

Texas Instruments TI-89 Specifications

General

Display size (HxV)	100 x 160 mm
Memory type	639K FLASH ROM, 188K bytes RAM
Compatible operating systems	Operating System 2.09
Battery type	AAA