Solve by Completing the Square x^2+14x+42=0

$x^{2} + 14 x + 42 = 0$

Step 1

Subtract $42$ from both sides of the equation.

$x^{2} + 14 x = - 42$

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 $b$ .

${(\frac{b}{2})}^{2} = {(7)}^{2}$

Step 3

Add the term to each side of the equation.

$x^{2} + 14 x + {(7)}^{2} = - 42 + {(7)}^{2}$

Step 4

Simplify the equation.

Simplify the left side.

Raise $7$ to the power of $2$ .

$x^{2} + 14 x + 49 = - 42 + {(7)}^{2}$

Simplify the right side.

Simplify $- 42 + {(7)}^{2}$ .

Raise $7$ to the power of $2$ .

$x^{2} + 14 x + 49 = - 42 + 49$

Add $- 42$ and $49$ .

$x^{2} + 14 x + 49 = 7$

Step 5

Factor the perfect trinomial square into ${(x + 7)}^{2}$ .

${(x + 7)}^{2} = 7$

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.

$x + 7 = \pm \sqrt{7}$

Subtract $7$ from both sides of the equation.

$x = \pm \sqrt{7} - 7$

Step 7

The result can be shown in multiple forms.

Exact Form:

$x = \pm \sqrt{7} - 7$

Decimal Form:

$x = - 4.35424868 \dots, - 9.64575131 \dots$