Solve by Completing the Square x^2+10x+15=0

$x^{2} + 10 x + 15 = 0$

Step 1

Subtract $15$ from both sides of the equation.

$x^{2} + 10 x = - 15$

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 $b$ .

${(\frac{b}{2})}^{2} = {(5)}^{2}$

Step 3

Add the term to each side of the equation.

$x^{2} + 10 x + {(5)}^{2} = - 15 + {(5)}^{2}$

Step 4

Simplify the equation.

Simplify the left side.

Raise $5$ to the power of $2$ .

$x^{2} + 10 x + 25 = - 15 + {(5)}^{2}$

Simplify the right side.

Simplify $- 15 + {(5)}^{2}$ .

Raise $5$ to the power of $2$ .

$x^{2} + 10 x + 25 = - 15 + 25$

Add $- 15$ and $25$ .

$x^{2} + 10 x + 25 = 10$

Step 5

Factor the perfect trinomial square into ${(x + 5)}^{2}$ .

${(x + 5)}^{2} = 10$

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.

$x + 5 = \pm \sqrt{10}$

Subtract $5$ from both sides of the equation.

$x = \pm \sqrt{10} - 5$

Step 7

The result can be shown in multiple forms.

Exact Form:

$x = \pm \sqrt{10} - 5$

Decimal Form:

$x = - 1.83772233 \dots, - 8.16227766 \dots$