Question 14211
Try this:

{{{ax^2 + bx + c = 0}}} Divide both sides by a.
{{{x^2 + (b/a)x + c/a = 0}}} Subtract c/a from both sides.
{{{x^2 + (b/a)x = -c/a}}} Now "complete the square" in x on the left side.
{{{x^2 + (b/a)x + (b/2a)^2 = (b/2a)^2 - c/a}}} Factor the left side.
{{{(x + b/2a)^2 = (b/2a)^2 - c/a}}} Simplify the right side and take the square root of both sides.
{{{x + b/2a = +-sqrt(b^2/4a^2 - c/a)}}} Simplify the radical.
{{{x + b/2a = +-sqrt((b^2 - 4ac)/4a^2)}}} Subtract b/2a from both sides.
{{{x = -b/2a +-sqrt(b^2 - 4ac)/2a}}} Simplify.
{{{x = (-b+-sqrt(b^2 - 4ac))/2a}}} Does this look familiar?