Final answer:
The expression c² + 6c + 9 factors completely as (c + 3)^2.
Step-by-step explanation:
To factor the expression c² + 6c + 9, we can rewrite it as (c + 3)(c + 3) or (c + 3)^2. This is because the expression matches the form of a perfect square trinomial, which always factors into the square of a binomial.
Learn more about Factoring a perfect square trinomial