Solve Using the Quadratic Formula (x-1)(x+8)=0

$(x - 1) (x + 8) = 0$

Step 1

Simplify the left side.

Simplify $(x - 1) (x + 8)$ .

Expand $(x - 1) (x + 8)$ using the FOIL Method.

Apply the distributive property.

$x (x + 8) - 1 (x + 8) = 0$

Apply the distributive property.

$x \cdot x + x \cdot 8 - 1 (x + 8) = 0$

Apply the distributive property.

$x \cdot x + x \cdot 8 - 1 x - 1 \cdot 8 = 0$

Simplify and combine like terms.

Simplify each term.

Multiply $x$ by $x$ .

$x^{2} + x \cdot 8 - 1 x - 1 \cdot 8 = 0$

Move $8$ to the left of $x$ .

$x^{2} + 8 \cdot x - 1 x - 1 \cdot 8 = 0$

Rewrite $- 1 x$ as $- x$ .

$x^{2} + 8 x - x - 1 \cdot 8 = 0$

Multiply $- 1$ by $8$ .

$x^{2} + 8 x - x - 8 = 0$

Subtract $x$ from $8 x$ .

$x^{2} + 7 x - 8 = 0$

Step 2

Use the quadratic formula to find the solutions.

$\frac{- b \pm \sqrt{b^{2} - 4 (a c)}}{2 a}$

Step 3

Substitute the values $a = 1$ , $b = 7$ , and $c = - 8$ into the quadratic formula and solve for $x$ .

$\frac{- 7 \pm \sqrt{7^{2} - 4 \cdot (1 \cdot - 8)}}{2 \cdot 1}$

Step 4

Simplify.

Simplify the numerator.

Raise $7$ to the power of $2$ .

$x = \frac{- 7 \pm \sqrt{49 - 4 \cdot 1 \cdot - 8}}{2 \cdot 1}$

Multiply $- 4 \cdot 1 \cdot - 8$ .

Multiply $- 4$ by $1$ .

$x = \frac{- 7 \pm \sqrt{49 - 4 \cdot - 8}}{2 \cdot 1}$

Multiply $- 4$ by $- 8$ .

$x = \frac{- 7 \pm \sqrt{49 + 32}}{2 \cdot 1}$

Add $49$ and $32$ .

$x = \frac{- 7 \pm \sqrt{81}}{2 \cdot 1}$

Rewrite $81$ as $9^{2}$ .

$x = \frac{- 7 \pm \sqrt{9^{2}}}{2 \cdot 1}$

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

$x = \frac{- 7 \pm 9}{2 \cdot 1}$

Multiply $2$ by $1$ .

$x = \frac{- 7 \pm 9}{2}$

Step 5

The final answer is the combination of both solutions.

$x = 1, - 8$

Solve Using the Quadratic Formula (x-1)(x+8)=0

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