I've been asked to factorise the following expression:

\(\displaystyle x^3 - x^2 - 4x + 2\)

From what I can tell, using the factor theorem (if f(a) = 0, then (x - a) is a factor of f(x)) and factors of 2 as input to the function, it can't be factorised. Am I right, can it not be factorised? When I'm asked a question like this, should I simply say "cannot be factorised"?

I'm not asking for answers, because this is for an assignment and I don't want to cheat, I'd just like to know whether I've come to the right conclusion or not.