y = x^3 + 2x^2 - 19x - 20
y = (x - 4)(x + 1)(x + 5)
My method: guess and check D:
You know the term without x has to be 20 so your numbers have to be factors that multiply to 20, and you go from there.
Assuming you meant
x / (x-5) + 9 / (x+1)
= (x^2 + 10x - 45) / (x-5)(x+1)
Find common denominator, change both fractions to have common denominator, then add.
(x+3) (x+5)(x-3)
------ x ----------
(x-3) (x+3)
x+3 and x-3 both cancel out (present in both top and bottom of the fraction)
Answer is x+5