Solve by Completing the Square x^2-8x=242

$x^{2} - 8 x = 242$

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.

$x^{2} - 8 x + {(- 4)}^{2} = 242 + {(- 4)}^{2}$

Step 3

Simplify the equation.

Simplify the left side.

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

$x^{2} - 8 x + 16 = 242 + {(- 4)}^{2}$

Simplify the right side.

Simplify $242 + {(- 4)}^{2}$ .

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

$x^{2} - 8 x + 16 = 242 + 16$

Add $242$ and $16$ .

$x^{2} - 8 x + 16 = 258$

Step 4

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

${(x - 4)}^{2} = 258$

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.

$x - 4 = \pm \sqrt{258}$

Add $4$ to both sides of the equation.

$x = \pm \sqrt{258} + 4$

Step 6

The result can be shown in multiple forms.

Exact Form:

$x = \pm \sqrt{258} + 4$

Decimal Form:

$x = 20.06237840 \dots, - 12.06237840 \dots$