posted by Adrian .
try some factors of 20
I tried ±1 and sure enough -1 worked, so x+1 is a factor
Then by either long division or synthetic division of x³-8x²+11x+20 by x+1
we would get x^2 - 9x + 20
which factors again into (x-4)(x-5)
so x³-8x²+11x+20 = (x+1)x-4)(x-5)