Synthetic division is one way to determine whether or not a given number is a root of the quadratic. x^2 − 12x − 20 can be rewritten as x^2 - 12x + 36 - 36 - 20, or (x - 6)^2 - 56, which does not have integer solutions:
(x - 6)^2 - 56 = 0 becomes (x - 6)^2 = 56, which works out to x - 6 = ± 2√14.
None of the possible roots suggested in this problem turns out to be an actual root.
