Question

Factor this polynomial completely x2 - x - 20

Answer 1

(x +5) (x -4)

Explanation:

Factors of 20:

1,20

2,10

4,5

4 and 5 combine to create 1

+5 -4 = 1

(x +5) (x -4)

Answer 2

(x+4)(x-5)

Explanation:

We can look at it by thinking of two numbers, that add up to -1 and multiply to -20. We can first do this by looking at factors of -20, which are 1, -20, -1, 20, 2, -10, -2, 10, and so on. After looking through it, we can notice that -5 and 4 added equal -1, and when multiplied equal to -20, so they work. So, we factor to (x+4)(x-5)