Solve Using the Quadratic Formula x^2-9x-36=0

$x^{2} - 9 x - 36 = 0$

Step 1

Use the quadratic formula to find the solutions.

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

Step 2

Substitute the values $a = 1$ , $b = - 9$ , and $c = - 36$ into the quadratic formula and solve for $x$ .

$\frac{9 \pm \sqrt{{(- 9)}^{2} - 4 \cdot (1 \cdot - 36)}}{2 \cdot 1}$

Step 3

Simplify.

Simplify the numerator.

Raise $- 9$ to the power of $2$ .

$x = \frac{9 \pm \sqrt{81 - 4 \cdot 1 \cdot - 36}}{2 \cdot 1}$

Multiply $- 4 \cdot 1 \cdot - 36$ .

Multiply $- 4$ by $1$ .

$x = \frac{9 \pm \sqrt{81 - 4 \cdot - 36}}{2 \cdot 1}$

Multiply $- 4$ by $- 36$ .

$x = \frac{9 \pm \sqrt{81 + 144}}{2 \cdot 1}$

Add $81$ and $144$ .

$x = \frac{9 \pm \sqrt{225}}{2 \cdot 1}$

Rewrite $225$ as $15^{2}$ .

$x = \frac{9 \pm \sqrt{15^{2}}}{2 \cdot 1}$

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

$x = \frac{9 \pm 15}{2 \cdot 1}$

Multiply $2$ by $1$ .

$x = \frac{9 \pm 15}{2}$

Step 4

The final answer is the combination of both solutions.

$x = 12, - 3$