Set f(x) = y -> y = x^2 + 6x +4 Now, subtract 4 from both sides. -> y - 4 = x^2 + 6x Complete the square (take half of six and square it) and add this to both sides. -> y - 4 + 9 = x^2 + 6x + 9 Now we can rewrite x^2 + 6x + 9 with a perfect square. -> y + 5 = (x + 3)^2 Subtract 5. -> y = (x + 3)^2 - 5
