x³ + 8x² + 11x - 20 ← the first on list
given the roots of a polynomial, say x = a, x = b and x = c
then the factors are (x - a), (x - b) and (x - c)
the polynomial is the product of the factors
f(x) = (x - a)(x - b)(x - c)
here x = - 5, x = - 4 and x = 1, hence factors are
(x + 5), (x + 4) and (x - 1)
f(x) =(x + 5)(x + 4)(x - 1) ← expanding factors gives
f(x) = (x² + 9x + 20)(x - 1) = x³ + 8x² + 11x - 20
