Question

Lamar is solving the equation x2−12x=−6 by completing the square. Which shows Lamar's next step and the solution to the equation?

Step 1: x^2 - 12x = -6

Step 2: x^2 - 12x + 36= -6 + 36

Answer 1

Completing the square is a process to find the solutions, or the x-values, to a quadratic equation. This method can only work if it is in the format: x^2 + bx = c
In this equation, the b value is -12 and the c value is -6. The process for completing the square goes like this:

x^2 + bx + (b/2)^2 = c + (b/2)^2

Now let’s solve the equation above using this method.

Step 1: x^2 - 12x + (-12/2)^2 = -6 + (-12/2)^2

Step 2: x^2 - 12x + (-6)^2 = -6 + (-6)^2

Step 3: x^2 - 12x + 36 = -6 + 36

Step 4: x^2 - 12x + 36 = 30

Now, to factor it. After doing the process until now, the left side of the equation can ALWAYS be in the format: (x + a)^2

Step 5: x^2 - 12x + 36 can be factored in this format as (x - 6)^2

Step 6: (x - 6)^2 = 30

Step 7: x - 6 = √30

Step 8: x = 6 ±√30