9.6.4 Solving Equations Using the Quadratic Formula

Algebra 19.6.4 Solving Equations Using the Quadratic Formula

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9.6.4 • Solving Equations Using the Quadratic Formula

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Here is the quadratic formula:

$x = \frac{- b \pm \sqrt{b^{2} - 4 a c}}{2 a}$

Use the formula to solve the equation $x^{2} + 9 x + 8 = 0$ .

Compare your answer:

The solutions are -8 and -1.

Apply the quadratic formula for $a = 1$ , $b = 9$ , $c = 8$ :

$x = \frac{- 9 \pm \sqrt{(9)^{2} - 4 (1) (8)}}{2 (1)} = \frac{- 9 \pm \sqrt{49}}{2}$ , which means

$x = \frac{- 9 - 7}{2} = - 8$ and $x = \frac{- 9 + 7}{2} = - 1$ .

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