Chapter 17: Activities
299
Box with Lid
Defining a Function
Take a 20 cm × 25 cm. sheet of paper and cut X × X squares from two corners. Cut X × 12½ cm
rectangles from the other two corners as shown in the diagram below. Fold the paper into a box
with a lid. What value of X would give your box the maximum volume V? Use the table and graphs
to determine the solution.
3. Press
2
¿ ƒ
A
ƒ
[:]
Ì
6
¿ ƒ
B
ƒ
[:]
5
¿ ƒ
C
Í
.
The coefficient of the x
2
term, the
coefficient of the X term, and the
constant for the new equation are stored
to A, B, and C, respectively.
4. Enter the quadratic formula using Classic
entry:
£ Ì ƒ
B
à y C ƒ
B
¡ ¹
4
ƒ
A
ƒ
C
~ ¤ ¥ £
2
ƒ
A
¤
.
Because the solution is a complex
number, you have to enter the formula
using the division operation instead of
using the
n/d
shortcut template. Complex
numbers are not valid in the
n/d
template
in input or output and will cause
Error: Data Type
to display.
5. Press
Í
to find one solution for the
equation 2x
2
N
6x + 5 = 0.
6. Press
}
to highlight the quadratic-
formula expression, and then press
Í
to paste it to the entry line.
7. Press
|
until the cursor is on the
+
sign
in the formula. Press
¹
to edit the
quadratic-formula expression to become
.
8. Press
Í
to find the other solution for
the quadratic equation: 2x
2
N
6x + 5 = 0.
