Question

Which factoring method would be best to factor x^2 - 9?

A perfect square trinomial method
B greatest common factor method
C trial and error
D difference and squares

Answer 1

D. difference of squares

Explanation:

Both of the terms x^2 and 9 are squares, so their difference is the difference of squares. The factorization of that is a "special form" that can be usefully memorized.

a^2 -b^2 = (a -b)(a +b)

x^2 -9 = (x -3)(x +3)