Which are factors of x2 – 4x – 5? check all that apply.
1.) (x – 5)
2.) (x – 4)
3.) (x – 2)
4.) (x + 1)
5.) (x + 5)

1.) (x-5) and 4.) (x+1). Factoring works as follows: x*x = x^2 and x*1=x and -5*x=-5x and -5*1=-5. So you then have, x^2+x+(-5x)+(-5), therefore, you get the original: x^2-4x-5. This is how factoring works. You could not have x-4 or x-3 for various reasons, including the fact that the only factors of 5 are 5 and 1.