Solve by Completing the Square x^2-8x=39

$x^{2} - 8 x = 39$

Step 1

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 2

Add the term to each side of the equation.

$x^{2} - 8 x + {(- 4)}^{2} = 39 + {(- 4)}^{2}$

Step 3

Simplify the equation.

Simplify the left side.

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

$x^{2} - 8 x + 16 = 39 + {(- 4)}^{2}$

Simplify the right side.

Simplify $39 + {(- 4)}^{2}$ .

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

$x^{2} - 8 x + 16 = 39 + 16$

Add $39$ and $16$ .

$x^{2} - 8 x + 16 = 55$

Step 4

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

${(x - 4)}^{2} = 55$

Step 5

Solve the equation for $x$ .

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

$x - 4 = \pm \sqrt{55}$

Add $4$ to both sides of the equation.

$x = \pm \sqrt{55} + 4$

Step 6

The result can be shown in multiple forms.

Exact Form:

$x = \pm \sqrt{55} + 4$

Decimal Form:

$x = 11.41619848 \dots, - 3.41619848 \dots$