The solutions of a quadratic equation are 5 and -1. What is the factored form of a related quadratic function?

a
f(x) = (x + 5)(x - 1)
b
f(x) = (x + 5)(x + 1)
c
f(x) = (x - 5)(x - 5)
d
f(x) = (x - 5)(x + 1)