Solve Using the Quadratic Formula x^2+5x-84=0

$x^{2} + 5 x - 84 = 0$

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 $a = 1$ , $b = 5$ , and $c = - 84$ into the quadratic formula and solve for $x$ .

$\frac{- 5 \pm \sqrt{5^{2} - 4 \cdot (1 \cdot - 84)}}{2 \cdot 1}$

Step 3

Simplify.

Simplify the numerator.

Raise $5$ to the power of $2$ .

$x = \frac{- 5 \pm \sqrt{25 - 4 \cdot 1 \cdot - 84}}{2 \cdot 1}$

Multiply $- 4 \cdot 1 \cdot - 84$ .

Multiply $- 4$ by $1$ .

$x = \frac{- 5 \pm \sqrt{25 - 4 \cdot - 84}}{2 \cdot 1}$

Multiply $- 4$ by $- 84$ .

$x = \frac{- 5 \pm \sqrt{25 + 336}}{2 \cdot 1}$

Add $25$ and $336$ .

$x = \frac{- 5 \pm \sqrt{361}}{2 \cdot 1}$

Rewrite $361$ as $19^{2}$ .

$x = \frac{- 5 \pm \sqrt{19^{2}}}{2 \cdot 1}$

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

$x = \frac{- 5 \pm 19}{2 \cdot 1}$

Multiply $2$ by $1$ .

$x = \frac{- 5 \pm 19}{2}$

Step 4

The final answer is the combination of both solutions.

$x = 7, - 12$