Question 116557
Completing the square means Take half the coefficient of the x term,
square it, and add it to both sides
{{{x^2 + 12x = -13}}}
{{{x^2 + 12x + (12/2)^2 = -13 + (12/2)^2}}}
{{{x^2 + 12x + 36 = -13 + 36}}}
{{{(x + 6)^2 = 23}}}
{{{x + 6 = 0 +-sqrt(23)}}}
{{{x = -6 +-sqrt(23)}}}