Question 668777
Consider the coefficient of the highest degree, call it Q.  Also consider the coefficient of the lowest degree (the constant) call it P. Find all factors of P and find all factors of Q , and take P/Q for each. Since Q is 1, this won't matter.

We get that the factors are {1,2,4,5,10,20}, plus or minus of course.
 
We are doing this because we want to find a 0 of the equation. So plug these different values until you get 0. It just so happens x =4.

Now do synthetic or long division:

(x^3-6x^2+13x-20)/(x-4) = x^2-2x +5

To finish this up, do the quadratic formula on x^2-2x+5 to obtain roots:

1-2i, 1+2i

Which means in factored form we have (x-4)(x-(1-2i))(x-(1+2i))