Answer:

(3y - 1)

Step-by-step explanation:

If you factor the (9y² - 1), the factors will be (3y+1) and (3y - 1).

To prove this, you can multiply my given factor using the foil method.

(3y+1)(3y-1) = ?

= 9y² - 3y + 3y - 1

= 9y² - 1