# What is the solution set for x^2 - 4x = 8?

Aug 15, 2015

Refer explanation

#### Explanation:

${x}^{2}$ - 4x - 8 = 0

Examine
${b}^{2}$ - 4ac
$- {4}^{2}$ - ($4 \times 1 \times - 8$) = 16 + 32 = 48 ( positive and not a perfect square . So use formula)

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

x = $\frac{- \left(- 4\right) \pm \sqrt{{\left(- 4\right)}^{2} - \left(4 \times 1 \times - 8\right)}}{2 \times 1}$

x = $\frac{4 \pm \sqrt{\left(16 - \left(- 32\right)\right)}}{2}$

x = $\frac{4 \pm \sqrt{16 + 32}}{2}$

x = $\frac{4 \pm \sqrt{48}}{2}$

x = $\frac{4 \pm 6.9}{2}$
x = $\frac{4 + 6.9}{2}$ = 5.45

x = $\frac{4 - 6.9}{2}$ = - 1.45