Answer: Choice C. (x+1)(x-5)
We need to find two numbers that
- Multiply to -5 (last term)
- Add to -4 (middle coefficient)
Through trial and error, those two numbers are 1 and -5
- 1 times -5 = -5
- 1 plus -5 = -4
So this means x^2-4x-5 factors to (x+1)(x-5)
This is the same as (x-5)(x+1) since the order of multiplication doesn't matter.
