Each of the options is a quadratic expression in vertex form. To rewrite the given expression in this form, the number 9 needs to be added to t he first two terms, because x2+6x+9 is equivalent to (x+3)2. Rewriting the number 4 as 9 – 5 in t he given expression yields x2+6x+9–5, which is equivalent to (x+3)2–5.