# How do you solve using the completing the square method  x^2+8x-9=0?

##### 1 Answer
Mar 18, 2016

Completing the square is designed to give you a perfect square trinomial on the left of an equation.

#### Explanation:

1. Get any constants on the right side.
${x}^{2} + 8 x = 9$

2. Add ${\left(\frac{b}{2}\right)}^{2} = {\left(\frac{8}{2}\right)}^{2}$ to both sides
${x}^{2} + 8 x + 16 = 9 + 16$

3. Factor the left.
${\left(x + 4\right)}^{2} = 25$

4. Square root both sides.
$\left(x + 4\right) = \pm 5$

5. $x = \left\{5 - 4 , - 5 - 4\right\} = \left\{1 , - 9\right\}$