Algebra Examples

$x^{2} - 8 x - 4 = 0$

Step 1

Add $4$ to both sides of the equation.

$x^{2} - 8 x = 4$

Step 2

To create a trinomial square on the left side of the equation, find a value that is equal to the square of half of $b$ .

${(\frac{b}{2})}^{2} = {(- 4)}^{2}$

Step 3

Add the term to each side of the equation.

$x^{2} - 8 x + {(- 4)}^{2} = 4 + {(- 4)}^{2}$

Step 4

Simplify the equation.

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Step 4.1

Simplify the left side.

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Step 4.1.1

Raise $- 4$ to the power of $2$ .

$x^{2} - 8 x + 16 = 4 + {(- 4)}^{2}$

Step 4.2

Simplify the right side.

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Step 4.2.1

Simplify $4 + {(- 4)}^{2}$ .

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Step 4.2.1.1

Raise $- 4$ to the power of $2$ .

$x^{2} - 8 x + 16 = 4 + 16$

Step 4.2.1.2

Add $4$ and $16$ .

$x^{2} - 8 x + 16 = 20$

Step 5

Factor the perfect trinomial square into ${(x - 4)}^{2}$ .

${(x - 4)}^{2} = 20$

Step 6

Solve the equation for $x$ .

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Step 6.1

Take the specified root of both sides of the equation to eliminate the exponent on the left side.

$x - 4 = \pm \sqrt{20}$

Step 6.2

Simplify $\pm \sqrt{20}$ .

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Step 6.2.1

Rewrite $20$ as $2^{2} \cdot 5$ .

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Step 6.2.1.1

Factor $4$ out of $20$ .

$x - 4 = \pm \sqrt{4 (5)}$

Step 6.2.1.2

Rewrite $4$ as $2^{2}$ .

$x - 4 = \pm \sqrt{2^{2} \cdot 5}$

Step 6.2.2

Pull terms out from under the radical.

$x - 4 = \pm 2 \sqrt{5}$

Step 6.3

Add $4$ to both sides of the equation.

$x = \pm 2 \sqrt{5} + 4$

Step 7

The result can be shown in multiple forms.

Exact Form:

$x = \pm 2 \sqrt{5} + 4$

Decimal Form:

$x = 8.47213595 \dots, - 0.47213595 \dots$