Algebra Examples

$(x + 9) (x - 10) = - 86$

Step 1

Move all terms to the left side of the equation and simplify.

Tap for more steps...

Step 1.1

Simplify the left side.

Tap for more steps...

Step 1.1.1

Simplify $(x + 9) (x - 10)$ .

Tap for more steps...

Step 1.1.1.1

Expand $(x + 9) (x - 10)$ using the FOIL Method.

Tap for more steps...

Step 1.1.1.1.1

Apply the distributive property.

$x (x - 10) + 9 (x - 10) = - 86$

Step 1.1.1.1.2

Apply the distributive property.

$x \cdot x + x \cdot - 10 + 9 (x - 10) = - 86$

Step 1.1.1.1.3

Apply the distributive property.

$x \cdot x + x \cdot - 10 + 9 x + 9 \cdot - 10 = - 86$

Step 1.1.1.2

Simplify and combine like terms.

Tap for more steps...

Step 1.1.1.2.1

Simplify each term.

Tap for more steps...

Step 1.1.1.2.1.1

Multiply $x$ by $x$ .

$x^{2} + x \cdot - 10 + 9 x + 9 \cdot - 10 = - 86$

Step 1.1.1.2.1.2

Move $- 10$ to the left of $x$ .

$x^{2} - 10 \cdot x + 9 x + 9 \cdot - 10 = - 86$

Step 1.1.1.2.1.3

Multiply $9$ by $- 10$ .

$x^{2} - 10 x + 9 x - 90 = - 86$

Step 1.1.1.2.2

Add $- 10 x$ and $9 x$ .

$x^{2} - x - 90 = - 86$

Step 1.2

Add $86$ to both sides of the equation.

$x^{2} - x - 90 + 86 = 0$

Step 1.3

Add $- 90$ and $86$ .

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

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

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

Step 4

Simplify.

Tap for more steps...

Step 4.1

Simplify the numerator.

Tap for more steps...

Step 4.1.1

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

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

Step 4.1.2

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

Tap for more steps...

Step 4.1.2.1

Multiply $- 4$ by $1$ .

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

Step 4.1.2.2

Multiply $- 4$ by $- 4$ .

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

Step 4.1.3

Add $1$ and $16$ .

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

Step 4.2

Multiply $2$ by $1$ .

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

Step 5

The result can be shown in multiple forms.

Exact Form:

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

Decimal Form:

$x = 2.56155281 \dots, - 1.56155281 \dots$