TI89-16
Chapt er 1
Copyright © Houghton Mifflin Company. All rights reserved.
Type on the entry line the difference
function, which is the profit function
S(t) – 0.001C(t). Press
ENTER .
Press
▲
and press and hold
►
to scroll to
the right to see the entire expression.
WARNING: If you do not get a symbolic result, it is because the variable you are using as the
input variable has a number stored in it. That is, the variable is a defined rather than an
undefined variable. The variable you use for the input variable must be an undefined variable
in order to obtain a symbolic result. Refer to the information at the top of page C-5 of this
Guide for more information.
To find the profit in 1998, evaluate the profit function at t
=2.
You can edit the entry line and replace t by 2 or you can enter
s(x)
−
0.001c(x)
in the
Y=
list and use the table. We find that the
profit in 1998 was P(2) ≈ 2.375 million dollars.
If you need to use the profit function for other calculations, you
may find it easier to define a new function,
p(t) = s(t)
−
0.001c(t)
andthenfind
p(2).
We illustrate the copy and paste feature of the
TI-89todothistask. Press
▲
until
s(t)
−
0.001c(t)
in the history
area is darkened.
Press
F1 [Tools] 5 [Copy].
Use
▼
to move the cursor to the
entry line and press
F1 [Tools] 6 [Paste].
Use
◄
to move the
cursor to the far left position in the entry line. Type
F4 [Other] 1
[Define] alpha
STO
(P) (
T
) =
and press
ENTER .
You can now find
p(2)
and/or enter
p(x)
in the
Y=
list so that you
can use the table to find other values, graph the function, and so
forth.
1.3.3 FI NDING A PRODUCT FUNCTION We illustrate this technique with the functions that
are given on page 32 of Section 1.3 of Calculus Concepts: Milk price = S(x) = 0.007x + 1.492
dollars per gallon on the xth day of last month and milk sales = G(x) = 31 – 6.332(0.921
x
)gal-
lons of milk sold on the xth day of last month.
You can, if you wish, define the functions s and g. (Note that the new definition for s will
replace the one defined in Section 1.3.3.) However, because we are only finding the product
function and only one output of it, we choose to name only the product function.
Find and define the product function with
F4 [Other]1[Define]
T
(
X
) = ( . 007
X
+ 1 . 492 )
( 31
−
6
. 332 ( . 921 ^
X
)
) ENTER .
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