x² - 6x + 9 =
(x - 3)(x - 3) or (x - 3)²
The factors would be (x - 3) and (x - 3).
If you need help factoring, you should talk to your teacher, but here's how I do it:
1. Look at the first term and its coefficient. Think of two possible numbers that would multiply to get the first term (i.e. 3x and 2x for 6x²) and put them first in the parentheses. You can also write all possible combinations on the side. However, this time, the only combination would be x and x multiplying to get x².
(x )(x )
2. Next, look at the last term. What two numbers multiply to get 9? Remember that two negative numbers can multiply to produce a positive one too. Basically, you're looking for two numbers that multiply to get 9 and add together to get -6. You might try all of the possible combinations, but none will work. In that case, you would go back to step 1 and try a different first term. In this case, though, there's only one combination for the first places, so that won't be necessary.
(x - 3)(x - 3)
Let me know if you have any more questions.