Solve Using the Quadratic Formula x(5x+18)=8

$x (5 x + 18) = 8$

Step 1

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

Simplify the left side.

Simplify $x (5 x + 18)$ .

Simplify by multiplying through.

Apply the distributive property.

$x (5 x) + x \cdot 18 = 8$

Reorder.

Rewrite using the commutative property of multiplication.

$5 x \cdot x + x \cdot 18 = 8$

Move $18$ to the left of $x$ .

$5 x \cdot x + 18 \cdot x = 8$

Multiply $x$ by $x$ by adding the exponents.

Move $x$ .

$5 (x \cdot x) + 18 \cdot x = 8$

Multiply $x$ by $x$ .

$5 x^{2} + 18 \cdot x = 8$

$5 x^{2} + 18 x = 8$

Subtract $8$ from both sides of the equation.

$5 x^{2} + 18 x - 8 = 0$

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 $a = 5$ , $b = 18$ , and $c = - 8$ into the quadratic formula and solve for $x$ .

$\frac{- 18 \pm \sqrt{18^{2} - 4 \cdot (5 \cdot - 8)}}{2 \cdot 5}$

Step 4

Simplify.

Simplify the numerator.

Raise $18$ to the power of $2$ .

$x = \frac{- 18 \pm \sqrt{324 - 4 \cdot 5 \cdot - 8}}{2 \cdot 5}$

Multiply $- 4 \cdot 5 \cdot - 8$ .

Multiply $- 4$ by $5$ .

$x = \frac{- 18 \pm \sqrt{324 - 20 \cdot - 8}}{2 \cdot 5}$

Multiply $- 20$ by $- 8$ .

$x = \frac{- 18 \pm \sqrt{324 + 160}}{2 \cdot 5}$

Add $324$ and $160$ .

$x = \frac{- 18 \pm \sqrt{484}}{2 \cdot 5}$

Rewrite $484$ as $22^{2}$ .

$x = \frac{- 18 \pm \sqrt{22^{2}}}{2 \cdot 5}$

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

$x = \frac{- 18 \pm 22}{2 \cdot 5}$

Multiply $2$ by $5$ .

$x = \frac{- 18 \pm 22}{10}$

Simplify $\frac{- 18 \pm 22}{10}$ .

$x = \frac{- 9 \pm 11}{5}$

Step 5

The final answer is the combination of both solutions.

$x = \frac{2}{5}, - 4$

Solve Using the Quadratic Formula x(5x+18)=8

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