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

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

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 $a = 2$ , $b = 1$ , and $c = - 1$ into the quadratic formula and solve for $x$ .

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

Step 3

Simplify.

Simplify the numerator.

One to any power is one.

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

Multiply $- 4 \cdot 2 \cdot - 1$ .

Multiply $- 4$ by $2$ .

$x = \frac{- 1 \pm \sqrt{1 - 8 \cdot - 1}}{2 \cdot 2}$

Multiply $- 8$ by $- 1$ .

$x = \frac{- 1 \pm \sqrt{1 + 8}}{2 \cdot 2}$

Add $1$ and $8$ .

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

Rewrite $9$ as $3^{2}$ .

$x = \frac{- 1 \pm \sqrt{3^{2}}}{2 \cdot 2}$

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

$x = \frac{- 1 \pm 3}{2 \cdot 2}$

Multiply $2$ by $2$ .

$x = \frac{- 1 \pm 3}{4}$

Step 4

The final answer is the combination of both solutions.

$x = \frac{1}{2}, - 1$