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386 Chapter 23: Activities
23ACTS.DOC TI-89/TI-92 Plus: Activities (English) Susan Gullord Revised: 02/23/01 1:24 PM Printed: 02/23/01 2:20 PM Page 386 of 26
Perform the following steps to derive the quadratic formula by
completing the square of the generalized quadratic equation.
1. Clear all one-character
variables in the current folder.
TI
-
89:
2ˆ
TI
-
92 Plus:
ˆ
Choose
1:Clear a-z
and press
¸
to confirm.
2. On the Home screen, enter the
generalized quadratic equation:
ax
ñ
+bx+c=0
.
3. Subtract
c
from both sides of
the equation.
TI
-
89:
2±|j
C
TI
-
92 Plus:
2±|
C
4. Divide both sides of the
equation by the leading
coefficient
a
.
5. Use the
expand()
function to
expand the result of the last
answer.
6. Complete the square by adding
((b/a)/2)
2
to both sides of the
equation.
Deriving the Quadratic Formula
This activity shows you how to derive the quadratic formula:
x =
ë
b
„
b
ñ
-
4ac
2a
Detailed information about using the functions in this example
can be found in Chapter 3: Symbolic Manipulation.
Performing
Computations to
Derive the Quadratic
Formula
Note: This example uses
the result of the last answer
to perform computations on
the
TI
-
89 / TI
-
92 Plus
. This
feature reduces keystroking
and chances for error.
Tip: Continue to use the las
t
answer
(
2±
)
as in step
3 in steps 4 through 9.