Step 1) Move all constants to the right side, leaving all of the terms with variables on the left side
x^2 - 12x = -28
Step 2) Find a number that would create a perfect square trinomial on the left side. For this problem, that would be 36. So, we need to add 36 to the left and right sides.
x^2 - 12x + 36 = -28 + 36
x^2 - 12x + 36 = 8
Step 3) Rewrite the perfect square trinomial on the left, so it only has two terms (becomes the square of itself)
(x - 6)^2 = 8
Step 4) Take the square root of both sides - remember that it is plus/minus because of the square!
x - 6 = ±
x - 6 = ±
Step 5) Find the two solutions of x
x = 6 +
x = -6 +
Hope this helps! :)