Texas Instruments TI-89, TI-92

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:

axñ+bx+c=0.

3. Subtract

c from both sides of

the equation.

TI-89: 2±|jC

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 = ëb „bñ-4ac

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

answer

(2±)

as in step

3 in steps 4 through 9.