Solve by Completing the Square x^2+8x-5=0

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

Step 1

Add $5$ to both sides of the equation.

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

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.

$x^{2} + 8 x + {(4)}^{2} = 5 + {(4)}^{2}$

Step 4

Simplify the equation.

Simplify the left side.

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

$x^{2} + 8 x + 16 = 5 + {(4)}^{2}$

Simplify the right side.

Simplify $5 + {(4)}^{2}$ .

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

$x^{2} + 8 x + 16 = 5 + 16$

Add $5$ and $16$ .

$x^{2} + 8 x + 16 = 21$

Step 5

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

${(x + 4)}^{2} = 21$

Step 6

Solve the equation for $x$ .

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

$x + 4 = \pm \sqrt{21}$

Subtract $4$ from both sides of the equation.

$x = \pm \sqrt{21} - 4$

Step 7

The result can be shown in multiple forms.

Exact Form:

$x = \pm \sqrt{21} - 4$

Decimal Form:

$x = 0.58257569 \dots, - 8.58257569 \dots$