Texas Instruments PLUS TI-89 - Manual (Page 403)

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: 2 ˆ
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 last
answer (
2 ± ) as in step
3 in steps 4 through 9.