note that if you do x = -a, you get so you can factor out (x--a) or (x+a).
so (x+a)*(x-5a) , because if you can factor out (x+a), and you do (x+a)*(x+b), then a*b = so b = -5a.
For any polynomial p(x), if you can find a root r, so p(r) = 0, then (x-r) divides p(x) with remainder 0. so you get p(x) = (x-r)*quotient .
but in your case using the quadratic formula can also solve this dilemna.
So for the quadratic formula which gives roots so (x--a)*(x-5a) also gives you the factorization.