When the X term is one, and doesn't have a leading coefficient, then you can factor it using the box and diamond method. look up videos on Khan Academy of the box and diamond method for solving trinomials. For number 9, you have a difference of squares. That means you can factor to just 2 terms. (x+4)(x-4) this works because 16 has an easy square root, and the sign in between is a negative(difference)