What is the factored form of x2 − 4x − 5?

a.(x + 5)(x − 1)
b.(x + 5)(x + 1)
c.(x − 5)(x − 1)
d.; (x − 5)(x + 1)

When the coefficient in front of the x^2 term is 1 you can factor a quadratic by finding two numbers such that the sum is the coefficient infront of x and the product is c. So
a+b=-4 and ab=-5 notice that -5 and 1 are solutions since (-5)*1=-5 and 1-5=-4 so you can factor it as (x-5)(x+1).