Solve Using the Quadratic Formula 5x^2-8x-4=0

$5 x^{2} - 8 x - 4 = 0$

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 $a = 5$ , $b = - 8$ , and $c = - 4$ into the quadratic formula and solve for $x$ .

$\frac{8 \pm \sqrt{{(- 8)}^{2} - 4 \cdot (5 \cdot - 4)}}{2 \cdot 5}$

Step 3

Simplify.

Simplify the numerator.

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

$x = \frac{8 \pm \sqrt{64 - 4 \cdot 5 \cdot - 4}}{2 \cdot 5}$

Multiply $- 4 \cdot 5 \cdot - 4$ .

Multiply $- 4$ by $5$ .

$x = \frac{8 \pm \sqrt{64 - 20 \cdot - 4}}{2 \cdot 5}$

Multiply $- 20$ by $- 4$ .

$x = \frac{8 \pm \sqrt{64 + 80}}{2 \cdot 5}$

Add $64$ and $80$ .

$x = \frac{8 \pm \sqrt{144}}{2 \cdot 5}$

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

$x = \frac{8 \pm \sqrt{12^{2}}}{2 \cdot 5}$

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

$x = \frac{8 \pm 12}{2 \cdot 5}$

Multiply $2$ by $5$ .

$x = \frac{8 \pm 12}{10}$

Simplify $\frac{8 \pm 12}{10}$ .

$x = \frac{4 \pm 6}{5}$

Step 4

The final answer is the combination of both solutions.

$x = 2, - \frac{2}{5}$