Activities 91
Performing Computations to Derive the Quadratic Formula
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.
@2 ˆ
Choose
1:Clear a-z and press ¸ to
confirm.
2. On the Home screen, enter the generalized
quadratic equation: ax
2
+bx+c=0.
3. Subtract c from both sides of the equation.
@ 2 ± | j C
Note: This example uses the result of the
last answer to perform computations on the
TI-89 Titanium. This feature reduces
keystroking and chances for error.
4. Divide both sides of the equation by the
leading coefficient
a.
Note: Continue to use the last answer (2
±) as in step 3 in steps 4 through 9.
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.
7. Factor the result using the
factor( )
function.
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