By trial and error method, find out that at x = -1, x3 + 13x2 + 32x + 20 = 0
Since x = -1 satisfies, therefore, x + 1 = 0 => (x+1) is a factor.
Divide x3 + 13x2 + 32x + 20 by (x+1)
You will get (x+1)(x2+12x+20) = x3 + 13x2 + 32x + 20
Factorising x2 + 12x + 20,
x2 + 10x + 2x + 20 = 0
(x + 2)(x + 10) = 0
So, the x3 + 13x2 + 32x + 20 = (x+1)(x+2)(x+10)