To factor x²-2x-4, you are looking to answer three questions.
1) What pair of numbers multiplies to 4?
2) What pair of numbers multiplies to 1?
3) Do these pairs when multiplied together, add/subtract to the middle term?
To answer (1), our pairs are 2 and 2, 4 and 1. Since there's a negative with 4 at the end (from question one), the signs will be opposite.
To answer (2), only pair multiplies to 1 - 1 and 1. Let's try both pairs from 1.
(x-4)(x+1) The middle term here is -3x. Nope.
(x-1)(x+4). The middle term here is 3x. Nope.
(x-2)(x+2) The middle term is 0x (or no middle term). Nope.
So x²-2x-4 does not factor.
