well i assumed that the factored form should have the same graph as the original equation but i didnt get the same graph. I have one question, what did you do to get (x+1)(x^3 - x^2 - 5x - 3)?
Since you know one root, you can use synthetic division on the polynomial. Also, you know that the only rational solutions are 1, -1, 3, -3, so you can look at those first, and see which of those are roots.