Solve Using the Quadratic Formula -20=-8x-x^2

$- 20 = - 8 x - x^{2}$

Step 1

Move all the expressions to the left side of the equation.

Add $8 x$ to both sides of the equation.

$- 20 + 8 x = - x^{2}$

Add $x^{2}$ to both sides of the equation.

$- 20 + 8 x + x^{2} = 0$

Step 2

Use the quadratic formula to find the solutions.

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

Step 3

Substitute the values $a = 1$ , $b = 8$ , and $c = - 20$ into the quadratic formula and solve for $x$ .

$\frac{- 8 \pm \sqrt{8^{2} - 4 \cdot (1 \cdot - 20)}}{2 \cdot 1}$

Step 4

Simplify.

Simplify the numerator.

Raise $8$ to the power of $2$ .

$x = \frac{- 8 \pm \sqrt{64 - 4 \cdot 1 \cdot - 20}}{2 \cdot 1}$

Multiply $- 4 \cdot 1 \cdot - 20$ .

Multiply $- 4$ by $1$ .

$x = \frac{- 8 \pm \sqrt{64 - 4 \cdot - 20}}{2 \cdot 1}$

Multiply $- 4$ by $- 20$ .

$x = \frac{- 8 \pm \sqrt{64 + 80}}{2 \cdot 1}$

Add $64$ and $80$ .

$x = \frac{- 8 \pm \sqrt{144}}{2 \cdot 1}$

Rewrite $144$ as $12^{2}$ .

$x = \frac{- 8 \pm \sqrt{12^{2}}}{2 \cdot 1}$

Pull terms out from under the radical, assuming positive real numbers.

$x = \frac{- 8 \pm 12}{2 \cdot 1}$

Multiply $2$ by $1$ .

$x = \frac{- 8 \pm 12}{2}$

Simplify $\frac{- 8 \pm 12}{2}$ .

$x = - 4 \pm 6$

Step 5

The final answer is the combination of both solutions.

$x = 2, - 10$