Texas Instruments TI-82 User Manual - Page 16

Defining a Function: Box with Lid - graph

Page 16 highlights

Defining a Function: Box with Lid Take a 200×250 mm. sheet of paper and cut X-by-X squares from two corners and X-by-125 mm. rectangles from the other two corners. Now fold the paper into a box with lid. What X would give the maximum volume V of a box made in this way? Use tables and graphs to determine the solution. Begin by defining a function that describes the volume of the box. From the diagram: 2X + A = W 2X + 2B = L V = A B X Substituting: V = (W - 2X) (L à 2 - X) X X WA X 1. Press z † Í to change the MODE back to Float. 2. Press y ãQuitä ' to return to the Home screen and clear it. 3. Press 200 ¿ ƒ W y ã:ä 250 ¿ ƒ L Í to store the width and length of the paper. 4. You define functions for tables and graphing on the Y= edit screen. Press o to access this screen. B XB L 5. Enter the function for volume as Y1. Press £ ƒ W ¹ 2 L ¥ 2 to define function Y1 in terms of X. („ lets you enter X quickly, without pressing ƒ.) The = sign is highlighted to show that Y1 is selected. 6 Getting Started

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6
Getting Started
Defining a Function: Box with Lid
Take a 200×250 mm. sheet of paper and cut X-by-X squares from two corners and
X-by-125 mm. rectangles from the other two corners. Now fold the paper into a
box with lid. What X would give the maximum volume V of a box made in this
way? Use tables and graphs to determine the solution.
Begin by defining a function that describes the
volume of the box.
From the diagram:
2X + A = W
2X + 2B = L
V = A B X
Substituting:
V = (W – 2X) (L
à
2 – X) X
W
X
X
A
B
X
B
L
1.
Press
z
Í
to change the
MODE
back
to
Float
.
2.
Press
y
ã
Quit
ä
to return to the Home
screen and clear it.
3.
Press
200
¿
ƒ
W
y
ã
:
ä
250
¿
ƒ
L
Í
to store the width and length of
the paper.
4.
You define functions for tables and graphing on
the
Y=
edit screen. Press
o
to access this
screen.
5.
Enter the function for volume as
Y
1
. Press
£
ƒ
W
¹
2
¤
£
ƒ
L
¥
2
¹
¤
Í
to define function
Y
1
in terms of
X
. (
lets you enter
X
quickly, without
pressing
ƒ
.)
The
=
sign is highlighted to show that
Y
1
is
selected.