Solve Using the Quadratic Formula 4x^2-8x-11=0

$4 x^{2} - 8 x - 11 = 0$

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 $a = 4$ , $b = - 8$ , and $c = - 11$ into the quadratic formula and solve for $x$ .

$\frac{8 \pm \sqrt{{(- 8)}^{2} - 4 \cdot (4 \cdot - 11)}}{2 \cdot 4}$

Step 3

Simplify.

Simplify the numerator.

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

$x = \frac{8 \pm \sqrt{64 - 4 \cdot 4 \cdot - 11}}{2 \cdot 4}$

Multiply $- 4 \cdot 4 \cdot - 11$ .

Multiply $- 4$ by $4$ .

$x = \frac{8 \pm \sqrt{64 - 16 \cdot - 11}}{2 \cdot 4}$

Multiply $- 16$ by $- 11$ .

$x = \frac{8 \pm \sqrt{64 + 176}}{2 \cdot 4}$

Add $64$ and $176$ .

$x = \frac{8 \pm \sqrt{240}}{2 \cdot 4}$

Rewrite $240$ as $4^{2} \cdot 15$ .

Factor $16$ out of $240$ .

$x = \frac{8 \pm \sqrt{16 (15)}}{2 \cdot 4}$

Rewrite $16$ as $4^{2}$ .

$x = \frac{8 \pm \sqrt{4^{2} \cdot 15}}{2 \cdot 4}$

Pull terms out from under the radical.

$x = \frac{8 \pm 4 \sqrt{15}}{2 \cdot 4}$

Multiply $2$ by $4$ .

$x = \frac{8 \pm 4 \sqrt{15}}{8}$

Simplify $\frac{8 \pm 4 \sqrt{15}}{8}$ .

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

Step 4

The result can be shown in multiple forms.

Exact Form:

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

Decimal Form:

$x = 2.93649167 \dots, - 0.93649167 \dots$