example: the second step in the process for factoring the trinomial x^2-3x-40 is to: Well you really should find the sum of the factors of −40 (not 40)
But before you can do that, you need to LIST the factors of −40 (not 40)
−1 * 40
−2 * 20
−4 * 10
−5 * 8
−8 * 5
−10 * 4
−20 * 2
−40 * 1
NOW we find the sum of the factors of −40
−1 + 40 = 39
−2 + 20 = 18
−4 + 10 = 6
−5 + 8 = 3
−8 + 5 = −3
−10 + 4 = −6
−20 + 2 = −18
−40 + 1 = −39
Then we choose the factors of −40 whose sum is −3 ---> −8 and 5
x^2 − 3x − 40 = (x − 8) (x + 5)
So FIRST step is B, SECOND step is C, and final step is factoring.
What Rita did was combine these 2 steps together, which you will learn to do as you get better at factoring.