Solve by Completing the Square x^2+18x=-45

$x^{2} + 18 x = - 45$

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 $b$ .

${(\frac{b}{2})}^{2} = {(9)}^{2}$

Step 2

Add the term to each side of the equation.

$x^{2} + 18 x + {(9)}^{2} = - 45 + {(9)}^{2}$

Step 3

Simplify the equation.

Simplify the left side.

Raise $9$ to the power of $2$ .

$x^{2} + 18 x + 81 = - 45 + {(9)}^{2}$

Simplify the right side.

Simplify $- 45 + {(9)}^{2}$ .

Raise $9$ to the power of $2$ .

$x^{2} + 18 x + 81 = - 45 + 81$

Add $- 45$ and $81$ .

$x^{2} + 18 x + 81 = 36$

Step 4

Factor the perfect trinomial square into ${(x + 9)}^{2}$ .

${(x + 9)}^{2} = 36$

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.

$x + 9 = \pm \sqrt{36}$

Simplify $\pm \sqrt{36}$ .

Rewrite $36$ as $6^{2}$ .

$x + 9 = \pm \sqrt{6^{2}}$

Pull terms out from under the radical, assuming positive real numbers.

$x + 9 = \pm 6$

The complete solution is the result of both the positive and negative portions of the solution.

First, use the positive value of the $\pm$ to find the first solution.

$x + 9 = 6$

Move all terms not containing $x$ to the right side of the equation.

Subtract $9$ from both sides of the equation.

$x = 6 - 9$

Subtract $9$ from $6$ .

$x = - 3$

Next, use the negative value of the $\pm$ to find the second solution.

$x + 9 = - 6$

Move all terms not containing $x$ to the right side of the equation.

Subtract $9$ from both sides of the equation.

$x = - 6 - 9$

Subtract $9$ from $- 6$ .

$x = - 15$

The complete solution is the result of both the positive and negative portions of the solution.

$x = - 3, - 15$

Solve by Completing the Square x^2+18x=-45

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