TI-89 Guide
TI89-17
Copyright © Houghton Mifflin Company. All rights reserved.
NOTE: You do not have to, but you can, use the times sign
between S and G to indicate the
product function. We enclosed each of S and G in parentheses to indicate a product when they
arewrittennexttoeachother,sothetimessignisnotnecessary.
To find milk sales on the 5th day of last month, evaluate
t(x)
at
x
= 5. On the entry line, type in
T
( 5)
and press
ENTER .
We find that milk sales were T(5) ≈ $40.93.
If you want to find the product function, copy the “Define t(x)”
statement and paste it into the entry line, press
◄
and use
►
until the cursor is just to the right of the = sign, and press
to
delete “Define t(x)=”. Press
ENTER .
1.3.4 CHECKI NG YOUR ANSWER FOR A COMPOSI TE FUNCTI ON We illustrate find-
ing a composite function with those functions given on page 33 of Section 1.3 of Calculus
Concepts: altitude = F(t)=
−
222.22t
3
+ 1755.95t
2
+ 1680.56t + 4416.67 feet above sea level
where t is the time into flight in minutes and air temperature = A(F) = 277.897(0.99984
F
)–66
degrees Fahrenheit where F is the number of feet above sea level. While the same technique that
we used to find the product function also can be used to find the composite function, for variety
we use a slightly different procedure.
Press
F1 (Y
=
)
and clear any previously entered functions.
Enter F in
y1
by pressing
(
−
)
222
. 22
X
^ 3+1755 . 95
X
^ 2+1680 . 56
X
+
4416
.
67
ENTER
and enter A in
y2
by pressing
277 . 897 ( . 99984 ^
X
) − 66
ENTER .
Enter the composite function (A
o
F)(x)=
A(F(x)) =
y2
(
y1(x)
)
in
y3.
Press
HOME .
Enter
y3(x)
on the entry
line to display the composite function.
WARNING: The TI-89 requires that you give the output symbol, not the function symbol,
when you refer to the formula that computes the output of a function. If you do not type
x
in
parentheses following
y3
, an argument error results.
•
Note that the symbolic form of the composite function contains e raised to a power, not
0.99984 raised to a power (as in
y2
). Converting between these two exponential forms is
discussed in Section 2.2 of Calculus Concepts.
1.3.5 TURNINGFUNCTIONSINTHEGRAPHINGLISTOFFANDON There are times
when you would like to keep the equations of certain functions in the
Y=
list but you do not
wantthemtographortobeshowninthetable. Anyfunctionthatisturnedonwillgraphand
will show in the TI-89 table. A function is turned on when a check mark appears next to it in
the
Y=
list and is turned off when there is no check mark next to it in the
Y=
list.
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