Solve Using the Quadratic Formula 4x^2-x-1=0

$4 x^{2} - x - 1 = 0$

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 $a = 4$ , $b = - 1$ , and $c = - 1$ into the quadratic formula and solve for $x$ .

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

Step 3

Simplify.

Simplify the numerator.

Raise $- 1$ to the power of $2$ .

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

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

Multiply $- 4$ by $4$ .

$x = \frac{1 \pm \sqrt{1 - 16 \cdot - 1}}{2 \cdot 4}$

Multiply $- 16$ by $- 1$ .

$x = \frac{1 \pm \sqrt{1 + 16}}{2 \cdot 4}$

Add $1$ and $16$ .

$x = \frac{1 \pm \sqrt{17}}{2 \cdot 4}$

Multiply $2$ by $4$ .

$x = \frac{1 \pm \sqrt{17}}{8}$

Step 4

The result can be shown in multiple forms.

Exact Form:

$x = \frac{1 \pm \sqrt{17}}{8}$

Decimal Form:

$x = 0.64038820 \dots, - 0.39038820 \dots$