How do you factorise the quadratic x2-9?

Answer 1

11

Answer 2

(x^2 - 9)

To factor this, we start off looking at the x^2. Since x^2 has no whole number in front of it (like 3x^2), then we know our factors are going to look like this:

(x );(x )

Now, what are the factors of -9? The factors of -9 are -1,1,-3,3,-9,9. Since our quadratic has no value that is multiplied by x [like (x^2 - 4x - 9)], then we know that the same numbers that multiply to make -9 must also add up to 0 (again, since there is no middle number multiplied by x). Therefore, the only factors of -9 that add to 0 and multiply to make -9 are... -3 and 3.

So, our factors are:

(x-3)(x+3)